NEVADA  AND  CALIFORNIA 


PROCESSES 


SILVER  AND  GOLD  EXTRACTION, 


FOR  GENERAL  USE,  AND  ESPECIALLY  FOR  THE 


MINING  PUBLIC  OF  CALIFORNIA  AND  NEVADA. 


WITH  FULL  EXPLANATIONS  AND  DIRECTIONS  FOR  ALL  METALLURGICAL 
OPERATIONS  CONNECTED  WITH  SILVER  AND  GOLD  FROM  A;-'- 
PRELIMINARY  EXAMINATION  OF  THE  ORE  TO 
THE  FINAL  CASTING  OF  THE  INGOT. 


ALSO, 


A  DESCRIPTION  OP  THE  GENERAL  METALLURGY  OF  SILYER  ORES, 

BY 

GUIDO  KUSTEL, 

Mining  Engineer  and  Metallurgist,  former  Manager  of  the  Ophir  Works,  etc. 


Illustrated  by  accurate  Engravings. 


SAN  FRANCISCO: 

FRANK   D  .  CAKLTON 
1  8  6  3. 


Entered  according  to  Act  of  Congress,  in  the  year  of  our  Lord  1863,  by 

FRANK  D.  CARLTON, 

In  the  Clerk's  office  of  the  District  Court  of  the  United  States  in  and  for  the  Northern 
District  of  California. 


Towne  &  Bacon,  Printers,  Excelsior  Office, 
No.  536  Clay  Street,  opposite  Leidesdorff. 


JrfWL 


The  rapid  extension  of  Silver  Mining  enterprise,  in  consequence 
of  numerous  discoveries  of  rich  and  extensive  silver-bearing  lodes 
in  California,  and  especially  in  Nevada  Territory,  has  excited  a 
general  desire  for  information  of  such  methods  of  extracting  Silver 
and  Gold  from  the  different  classes  of  ores,  as  are  practical  and 
adapted  to  our  circumstances. 

In  representing  the  different  modes  of  working  silver  ores,  it 
appeared  a  necessity  in  some  cases  to  treat  the  theory  fully,  as  for 
instance  concerning  the  roasting  process,  which  it  is  impossible  to 
carry  on  for  certain  purposes,  if  the  mutual  action  of  the  various 
substances,  under  the  influence  of  heat,  is  not  well  understood.  In 
regard  to  this  point  I  am  indebted  for  valuable  information  to  "  F. 
Plattner,  on  Roasting  Processes." 

I  have  prepared  the  text  of  this  work  with  care,  and  supplied 
the  first  part  with  distinct  and  detailed  drawings,  so  that  one  by 
studying  it  can  learn  to  perform  all  the  operations.  If,  however, 
there  are  yet  many  things  not  satisfactorily  explained,  or  not 
thoroughly  treated,  it  may  be  attributed  to  the  circumstance  that 
our  metallurgy  is  very  young. 

The  second  part  contains  a  description  of  the  general  metallurgy 
of  silver  ores,  for  which  I  am  indebted  to  Kert's  Metallurgy, 
one  of  the  latest  and  best  German  works.  It  is  not  likely  that 
melting  or  precipitation  will  ever  be  introduced  in  California  or 


4 


PREFACE. 


Nevada  for  general  use,  yet,  under  particular  circumstances,  in 
one  case  or  another,  it  may  in  future  prove  useful  to  adopt  proc- 
esses, which  are  not  practiced  here  at  present.  For  this  and  other 
reasons  a  brief  but  careful  description  of  the  general  metallurgy 
of  silver  ores  is  given. 

The  assaying  of  ores,  tailings,  bullion-metal,  etc.,  is  so  closely 
connected  with  the  mill  and  mining  business  that  tables  showing 
the  amount  of  fine  metal  per  ton  of  ore  and  also  the  value  of  silver 
and  gold  per  ounce  at  different  degrees  of  fineness  have  been 
added  for  reference. 
Dayton,  N.  T.,  May,  1863. 


TABLE  OF  CONTENTS. 


PART  FIRST. 


Chapter  I. 

Page. 


Remarks  on  the  Blowpipe   9 

Blowpipe  Tools   10 

Blowpipe  Reagents   10 

Blowpipe  Instruments   12 

Blowpipe  Materials   14 

Blowpipe  Use   15 

Blowpipe  Examination  on  Charcoal.  16 
Blowpipe  Examination  on  Charcoal 

with  Soda  and  Borax   18 

Blowpipe  Examination  in  a  closed 

Glass  Tube   20 

Blowpipe  Examination  in  an  open 

Glass  Tube   22 

Systematic  Procedure  for  the  Determ- 
ination of  Gold  and  Silver  Minerals  23 
Analysis  of  retorted  Amalgam  or  Bul- 
lion  26 

Blowpipe  Assay   28 

Specific  Gravity   33 

Hardness.   35 

Chapter  II. 

DESCRIPTION  OF  GOLD  ORES. 

Gold   36 

Gold  in  Combination  with  Silver   36 

Gold  in  Combination  with  Tellurium..  37 
Gold  in  Combination  with  Tellurium 

and  Lead   37 

Gold  in  Combination  with  Mercury 

and  Silver   37 

DESCRIPTION  OF  SILVER  ORES. 

Native  Silver   38 

Silver  Glance  (Sulphuret  of  Silver). ..  38 

Stromeyerite  (Silver-copper  Glance)..  39 


Page. 


Sternbergite   39 

Sternbergite  of  Gold  Hill   39 

Brittle  Silver  Ore   40 

Polybasite   40 

Miargyrite   41 

Dark  Red  Silver  Ore  (Ruby  Silver) 41 

Light  Red  Silver  Ore  (Ruby  Silver) ..  42 

Xanthocone   42 

Silver  Fahlerz  (Argentiferous  Gray 

Copper  Ore   42 

Horn  Silver  (Chloride  of  Silver)   43 

Embolite  (Chlorobromide  of  Silver)..  44 

Bromyrite   44 

Iodyrite   44 

Iodid  of  Mercury  and  Silver   45 

Antimonial  Silver   45 

Naumannite  (Selenid  of  Silver)   46 

Eucairite   46 

Hessite  (Tellurid  of  Silver)   46 

Bismuth  Silver   47 

Silver  Amalgam   47 

Arquerite   47 

Chapter  III. 

Fire  Assay   48 

Tools   48 

Materials   49 

Gold  and  Silver  Assay   50 

Lead  Assay   57 

Chapter  IV. 

Extraction  of  Gold   59 

Remarks   59 

Amalgamation  in  the  Battery   59 

Amalgamation  on  Copper  Plates ...  61 


6 


CONTENTS. 


Page. 

Amalgamation  in  Arrastras   61 

Amalgamation  in  Pans   63 

Extraction  of  Gold  by  Clilorination.-  64 

Chapter  V. 

Extraction  of  Silver   67 

Division  of  Processes   67 

Wet  Process   67 

Chemicals   69 

Sulphate  of  Copper   69 

Sulphate  of  Iron   71 

Bisulphate  of  Soda   71 

Alum   71 

Sulphuric  Acid   71 

Salt,  Common   72 

Chloride  of  Copper   72 

Subchloride  of  Copper   73 

Protochloride  of  Iron   73 

Chloride  of  Iron   74 

Chemicals,  quantity  per  Ton  of  Ore.  74 

Amalgamation  in  Pans   76  i 

Amalgamation  in  Wheeler's  Pans...  81  | 

Roasting  Process   90 

Behavior  of  Chlorine   94 

Behavior  of  Hydrochloric  Acid   96  ! 

Behavior  of  Salt   96 

Roasting,  remarks   98 

Roasting  for  the  Barrel  and  Veatch's 

Amalgamation   101 

Roasting  for  Pan  Amalgamation   106 

Roasting  of  Silver  Ores  rich  in  Anti- 
mony  110 

Roasting  in  a  Mechanical  Furnace..  114 


Page. 

Loss  of  Silver  in  Roasting  115 

Amalgamation  in  Barrels   117 

Amalgamation  in  Veatch's  Steam 

tubs   122 

Amalgamation  in  Pans   124 

Cold  Process   128 

Patio  or  American  Heap  Amalgama- 
tion 128 

Retorting   132 

Melting   134 

Assay  of  the  Bar   143 

Melting  Process   145 

Melting   154 

Mixture  of  Ore  and  Fluxes   151 

Separation  of  Lead  and  Silver  154 

Refining   162 

Pattiuson's  Process   164 

Chapter  VI. 

Description  of  the  Common  Pan  169 

Description  of  Wheeler's  Pan   170 

Description  of  Wheeler's  Agitator.. ..  173 
Description  of  Hepburn  &  Peterson's 

Pan   174 

Description  of  Roasting  Furnace  176 

Description  of  Mechanical  Roasting 

Furnace   177 

Description  of  Retort   178 

Description  of  Crucible  Furnace   179 

Description  of  the  Melting  Furnace..  180 
Description  of  the  Cupelling  Furn- 
ace   183 

Description  of  the  Refining  Furnace..  186 


PART  SECOND. 

GENERAL  METALLURGY  OF  SILVER  ORES. 


Chapter  I. 
Silver  Ores,  extensively  used  for  Ex- 


traction  189 

Argentiferous  Lead  Ores   190 

Argentiferous  Copper  Ores   190 

Argentiferous  Zinc  Ores   191 

Argentiferous  Iron  and  Magnetic 

Pyrites   191 

Assays   191 

Dry  or  Fire  Assays   192 

Assays  of  Rich  Ores   193 

Assays  of  Poor  Ores   196 


Assays  of  Argentiferous  Alloys   197 


Wet  Assays   199 

Blowpipe  Assays   199 

Chapter  II. 

Methods  of  extracting  Silver   205 

Melting  with  Lead  or  Lead  Ores. ..  205 

Amalgamation   207 

Dissolution  and  Precipitation   208 

Division  of  principal  Methods  of  Ex- 
traction   211 


Chapter  III. 
Extraction  of  Silver  in  the  Dry  Way.  216 


CONTENTS. 


7 


Page. 


Extraction  with  Lead  216 

Production  of  Argentiferous  Lead.-  220 

Melting  in  Crucibles  220 

Melting  in  the  Cupelling  Furnace...  221 
Melting  with  Unroasted  Lead  Ores.  222 
Melting  of  Argentiferous  Lead  Ores.  223 
Melting  of  Argentiferous  Copper 

Ores  224 

Lead  Manipulation  with  Matts   225 

Concentration  of  Silver  in  Matt....  225 

Extraction  from  Matts  by  Lead  228 

Liquation  231 

Cupellation  235 

Cupellation  inunmovable  hearths...  235 

Cupellation  in  movable  hearths  243 

Pattinson's  Process   244 

Parke's  Process  249 

Refining  of  Silver  251 

Refining  on  Movable  Tests  254 

Refining  under  Muffles  255 


Page. 


Refining  at  the  Mint  of  Clausthal...  257 
Refining  in  Reverberatory  Furnaces.  257 
Refining  in  Crucibles  259 

Extraction  of  Silver  in  the  Wet  Way.  261 

Amalgamation  in  Barrels  262 

Roasting   263 

Amalgamation  of  Ores  265 

Amalgamation  of  Copper  Matt  267 

Amalgamation  of  Speiss  268 

Amalgamation  of  Black  Copper  268 

Augustin's  Process  270 

Augustin's  Process  on  Matts   270 

Ziervogel's  Process  275 

Patera's  Process  279 

Tables  showing  the  Amount  of  Fine 
Metal  per  Ton  of  Ore  283 

Tables  showing  the  Value  of  Silver  per 
Ounce  in  the  Bar   297 

Tables  showing  the  Value  of  Gold  per 
Ounce  in  the  Bar  311 


EERATA. 


Page  70,  bottom  line,  for  30-100  read  30-1000. 

72,  line  1,  for  condition.  In  read  condition,  in. 
149,  "  16,  for  sulphurets  read  sulphates. 
161,  "    6,  for  as  off  read  off  as. 
163,  "  20,  for  can  be  read  cannot  be. 
171,  "  18,  for  ledge  read  edge. 
190,  "    9,  for  rich  read  richer. 
192,  "    3,  for  fast  read  first. 
203,  "  14,  for  block  read  black. 
217,  "   4,  for  lead  crucibles  read  lead  in  crucibles. 
221,  "  24,  for  hesth  read  hearth. 
231,  "  20,  for  silver  containing  read  silver-containing. 
241,  "  16,  for  silver  read  sides. 
248,  bottom  line,  for  crystallization  read  cupellation. 
269,  line  17,  for  oxyd  read  mixed. 


CHAPTER  I. 


The  knowledge  of  the  composition  of  different  classes 
of  gold  and  silver  ores  is  of  great  importance  to  every 
miner,  especially  to  the  millman.  This  knowledge  is 
easily  acquired  by  the  aid  of  the  blowpipe.  I  have 
endeavored  to  show  the  use  of  the  blowpipe,  limited  to 
gold  and  silver  ores,  with  as  few  and  simple  instruments 
as  possible.  The  blowpipe  is  a  very  insignificant  look- 
ing instrument;  but  a  short  acquaintance  with  it  will 
show  that  no  person  engaged  in  mining  can  get  along 
without  it,  no  matter  whether  he  be  a  good  judge  of  ore 
or  not.  There  are  many  different  kinds  of  silver  ores, 
the  richness  of  which  cannot  be  determined  by  the  eye 
of  the  best  judge. 

Long  study  and  extensive  apparatus  are  necessary  to 
learn  the  mode  of  making  the  wet  analysis,  and  the 
application  demands  much  time  and  patience  in  every 
instance.  This  proves  unsuited  to  the  general  use  of 
the  millman.  But  the  use  of  the  blowpipe  is  acquired 
in  a  short  time,  and  half  an  hour's  blowing  upon  a  piece 
of  ore  will  tell  us  all  about  what  it  is,  or  how  much 
silver  it  contains. 


10  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

The  instructions  in  regard  to  the  use  of  the  blowpipe 
in  this  book  refer  only  to  such  gold  and  silver  ores  as 
are  described  herein. 

APPARATUS  AND  RE-AGENTS 
For  Analysis  of  Gold  and  Silver  Ores  by  the  Blowpipe. 

TOOLS. 

Section  1.  A  Blowpipe. — A  proper  blowpipe  must 
have  a  chamber  to  receive  the  condensed  water,  and 
should  have  a  mouth-piece  of  horn  or  ivory,  without 
which  long  blowing  is  very  tiresome  ;  a  common  alcohol 
lamp  ;  a  small  agate  or  porcelain  mortar  with  pestle  ;  a 
magnifying  glass  ;  a  small  magnet ;  a  small  hammer  and 
square  piece  of  steel  to  serve  as  an  anvil ;  a  steel  for- 
ceps ;  a  small  file  and  glass  tubes.  It  is  best  to  procure 
glass  tubes  in  pieces  two  or  three  feet  long,  about  three- 
sixteenths  of  an  inch  in  the  clear.  They  are  cut  with 
the  file  into  pieces  four  and  eight  inches  long,  of  which 
the  shorter  ones  are  ready  for  use,  being  open  at  both 
ends.  The  eight-inch  pieces  are  held  in  the  alcohol 
flame  with  the  fingers  at  each  end.  When  the  tube  gets 
red-hot  in  the  middle,  it  will  part  into  two  pieces  by 
drawing,  forming  tubes  closed  at  one  end. 

RE-AGENTS. 

Sec.  2.  1.  Carbonate  of  Soda. — It  makes  no  difference 
whether  carbonate  or  bicarbonate  of  soda  is  used,  but  it 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  11 

must  be  free  from  sulphuric  acid.  To  ascertain  the 
absence  of  sulphuric  acid,  a  small  portion  of  the  soda 
may  be  melted  with  the  blowpipe  on  charcoal,  till  it 
draws  into  the  coal.  This  part  is  then  broken  out  with 
a  penknife,  put  on  a  blank  spot  of  a  silver  coin,  and 
moistened  with  water.  After  one  or  two  minutes  it  is 
removed.  If  the  soda  contains  any  sulphuric  acid,  a 
yellow  or  brown  spot  will  be  seen  on  the  silver.  In  this 
case  the  soda  must  be  purified,  which  may  be  done  in 
the  following  way  :  The  pulverized  bicarbonate  is  intro- 
duced into  a  glass  funnel  on  a  piece  of  filtering  paper, 
double  folded,  under  which  some  loose  cotton  was  placed. 
Cold  distilled  water  is  poured  over  it  several  times,  till 
the  soda  is  sufficiently  washed.  This  can  be  ascertained 
by  trying  a  little  on  charcoal,  as  before  described.  This 
soda  is  used  for  the  detection  of  small  quantities  of  sul- 
phur. 

2.  Borax. — The  borax  of  commerce  is  generally  pure 
enough  to  serve  the  purpose.  A  small  piece,  melted  on 
charcoal,  if  pure,  will  turn  into  a  colorless  glass  pearl. 
If  it  appears  colored,  the  borax  must  be  purified,  by 
dissolving  it  in  hot  water,  and  subsequently  crystallizing 
it.  The  borax  has  the  property  to  dissolve  oxyds  of 
metals  when  melted  with  them,  assuming  different  colors. 
By  this  treatment,  several  metals  are  recognized. 

3.  Bisalphate  of  Potassa. — This  is  easily  prepared.  One 
ounce  of  sulphate  of  potassa,  roughly  ground,  and  half 


12  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

an  ounce  of  sulphuric  acid,  are  heated  in  a  porcelain 
cup  by  the  alcohol  lamp  till  all  is  in  a  quiet,  transparent 
fluid  condition.  The  cup  is  then  taken  from  the  fire, 
and  the  contents  poured  on  a  piece  of  sheet  iron.  The 
bisulphate  of  potassa  is  used  in  testing  ore  for  iodine 
and  bromine. 

4.  Tin. — The  tinfoil  is  used  to  discover  a  small  quan- 
tity of  copper  in  the  ore.  The  tin  has  the  property  of 
reducing  oxyds  of  metals  to  a  lower  state  of  oxyd  in 
glass  fluxes,  effecting  thus  a  different  appearance,  by 
which  the  metal  can  be  recognized  more  easily. 

5.  Oxyd  of  Copper. — A  piece  of  clean  copper  is  dis- 
solved in  nitric  acid,  evaporated  to  dryness,  and  heated 
by  degrees  in  a  small  porcelain  cup  to  red  heat.  It  is 
used  for  the  detection  of  chlorine. 

APPARATUS  AND  RE-AGENTS 
For  Blowpipe  Assays. 

INSTRUMENTS. 

Sec.  3.  1.  An  Assay  Balance* — This  is  the  most  expen- 
sive necessary  instrument.  The  best  for  our  purpose  is 
the  blowpipe  balance,  which  answers  also  perfectly  for 
the  fire  and  bar  assays.  Such  a  balance  costs  from  one 
hundred  to  one  hundred  and  twenty  dollars. 


*  Good  ones  are  made  by  W.  Schmoltz,  in  San  Francisco,  from  seventy-five 
to  eighty  dollars. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  13 

The  weights  should  be  grain  weights  (Troy).  Ten 
grains  represent  the  unit,  which  is  divided  into  :  1,000, 
400,  300,  200,  100,  40,  30,  20,  10,  4,  3,  2, 1  thousandths. 

A  little  spoon,  of  the  size  of  an  ear-pick,  made  of 
ivory  or  copper,  to  weigh  out  the  powdered  ore.  The 
handle  of  this  spoon  should  have  the  form  of  a  spatula, 
for  mixing  ore  with  lead  and  borax  glass  in  the  capsule. 

A  small  wooden  solid  cylinder,  to  make  paper  tubes,  in 
which  the  assay  is  packed  and  melted  (Fig.  1  a).  The 
paper  tubes  are  made  best  of  fine  letter  paper,  which  is 
cut  into  strips  one  and  one-half  inches  by  one.  The  strip 
(Fig.  1  b)  is  rolled  round  the  cylinder,  so  that  the  long 
side  of  the  paper  may  project  beyond  the  end  of  the 
cylinder,  the  distance  of  its  diameter.  The  projected 
part  is  pressed  down  where  the  strip  ends  with  the  aid 
of  the  handle  of  the  small  spoon,  then  the  left  and  right 
side,  and  finally  the  remainder.  The  cylinder  is  then 
turned,  and  the  folded  end  knocked  on  the  table  two  or 
three  times.  The  tube  is  taken  off,  and  is  ready  to  be 
used. 

A  drill  to  bore  holes  in  the  charcoal,  in  which  the 
paper  tube  with  the  ore  is  placed  to  be  melted.  This 
drill  (Fig  2)  has  the  shape  of  a  cross,  or  a  double  chisel 
crossing  at  right  angles,  and  must  be  a  little  larger  than 
the  cylinder  (Fig.  1). 

A  brass  capsule,  of  the  shape  as  represented  in  Fig.  3. 
It  is  two  and  one-half  inches  long.  At  the  line  a  one- 
eighth  of  an  inch  deep,  and  one-fourth  of  an  inch  wide. 
At  the  line  b,  one-fourth  of  an  inch  deep,  and  seven- 


14  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

eighths  wide.  This  capsule  serves  for  mixing  ore  with 
fluxes. 

A  cupel  holder  (Fig.  4  a),  is  made  of  copper  or  brass ; 
its  size  according  to  the  size  of  the  cupels. 

Cupels  (Fig.  4  b),  made  of  boneash.  The  smallest 
kind  will  answer. 

MATERIALS. 

Sec.  4.  1.  Borax. The  borax  for  blowpipe  assays  is 
used  as  borax  glass.  A  black  lead  or  other  crucible  is 
made  red-hot,  and  some  borax  introduced.  It  will  swell 
up  at  first,  and  then  melt  down.  The  borax  is  added  in 
small  portions,  till  the  required  quantity  is  obtained. 
The  fluid  borax  is  poured  on  a  clean  iron  plate,  pulver- 
ized, and  kept  in  a  bottle  with  a  ground  glass  stopple. 
If  exposed  to  the  air,  it  absorbs  moisture,  and  is  unlit  for 
our  purpose. 

2.  Lead.^- The  lead  must  be  perfectly  free  from  silver. 
Pure  lead  can  be  obtained  in  the  following  way :  Ace- 
tate of  lead  is  dissolved  in  hot  water  and  filtered.  A 
piece  of  clean  zinc  will  precipitate  the  lead.  This  must 
be  washed  several  times  with  clean  water,  in  order  to 
get  rid  of  the  zinc,  which  is  now  in  solution.  The  lead 
is  then  dried  and  melted  in  a  clean  crucible  with  some 
soda  and  borax.  Small  quantities  of  lead  cannot  well 
be  granulated  ;  it  is  then  better  to  file  it.* 


*  Scales,  balances,  tools,  assay  apparatus,  and  all  chemicals  mentioned  in  this 
work,  are  to  be  found  at  John  Taylor's,  Washington  Street,  San  Francisco. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


15 


USE  OF  THE  BLOWPIPE. 

Sec.  5.  The  only  difficulty  which  some  beginners 
find  in  using  the  blowpipe  is  the  production  of  a  contin- 
ual blast.  To  effect  this,  one  must  blow  the  air  by  aid 
of  the  cheeks,  and  supply  the  mouth  with  air  by  the 
lungs.  The  breathing  must  continue  through  the  nose 
during  the  blowing.  The  direct  use  of  the  lungs  for 
the  blowpipe  must  be  avoided,  as  it  injures  the  chest. 

The  flame  shows  two  different  parts  of  different  char- 
acter. If  the  blowpipe  is  kept  so  that  the  point  touches 
the  flame  of  the  candle,  as  represented  in  Fig.  5  a,  it 
produces  a  yellow  inner  flame,  which  has  the  prop- 
erty of  preventing  oxydation,  on  account  of  its  amount 
of  carbon.  It  effects  the  reduction  of  many  oxyds  of 
metals,  and  is  called  the  reduction  flame.  It  must  be 
used  so  as  to  cover  the  test  particle  (Fig.  5  b). 

The  other,  the  outer  flame,  is  produced  by  holding  the 
blowpipe  point  a  little  into  the  flame,  above  the  wick 
(Fig.  6  c).  This  outer  flame  is  blue,  sharp-pointed,  and 
must  be  free  of  yellow  parts.  It  has  the  reverse  prop- 
erty of  the  inner  flame,  oxydizing  the  metals  when  before 
the  blue  point  (Fig.  6  e). 

The  wick  of  the  candle  must  be  kept  short,  and  the 
end  bent  down  like  a  hook.  Particles  of  thread  or  other 
matters  on  the  wick  are  removed,  because  they  interfere 
with  the  purity  of  the  flame. 


16  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


EXAMINATION  ON  CHARCOAL. 

Sec.  6.  In  examining  the  ore  on  charcoal,  attention 
must  be  paid  first  to  the  odor,  then  to  the  coating  by  the 
volatile  metals  or  oxyds  of  metals.  The  grain,  taken 
into  examination  must  be  small,  about  the  size  of  the 
button  represented  by  e  in  Fig.  6.  The  charcoal  must 
be  sawn  lengthwise.  On  a  flat  surface  a  small  hole  is 
made  near  the  edge  with  a  penknife,  to  receive  the  par- 
ticle of  ore  intended  for  the  test. 

The  ore  may  be  blown  at,  first  with  the  outer  or  oxy- 
dation  flame.  If  the  ore  decrepitates,  it  must  be  pulver- 
ized in  the  agate  mortar.  As  soon  as  the  test  gets  red 
hot,  the  odor  must  be  observed.  Sulphur  emits  sulphur- 
ous acid,  a  well-known  odor.  Selenium  has  a  disagree- 
able smell,  somewhat  like  rotten  radish,  and  the  arsenic 
is  recognized  by  the  garlic-like  odor.  If  sulphur  is  pres- 
ent, a  small  amount  of  arsenic  could  not  be  detected. 
In  this  case  the  reduction  flame  is  applied,  after  no  more 
odor  of  sulphurous  acid  is  observed,  and  recognized  by 
the  odor. 

Next,  the  attention  should  be  directed  to  the  coating 
of  charcoal  by  volatile  combinations.  It  is  of  import- 
ance to  notice  the  distance  of  the  coating  from  the  test, 
and  also  the  color,  which  generally  changes  on  cooling. 
Some  coating  when  played  upon  with  the  oxydation 
flame,  will  move  from  one  place  to  another,  or  will 
cause  a  colored  halo,  when  treated  with  the  reduction 
flame.    It  is  necessary,  therefore,  to  get  acquainted 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  17 

with  the  different  coatings  produced  by  different  metals, 
not  only  those  composing  the  gold  and  silver  ores,  de- 
scribed in  this  book,  but  also  others,  which  appear  some- 
times in  the  silver  ores,  though  not  essential  to  their 
classification. 

Lead — Gives  a  coating  with  both  flames  near  the 
assay.  It  appears  dark  lemon  yellow  when  hot,  changes 
into  sulphur  yellow  when  cold.  In  thin  layers  it  ap- 
pears bluish  white.  The  coating  may  be  driven  away 
by  both  flames,  coloring  the  reduction  flame  blue.  If 
iodine  be  present,  the  coating  is  far  off  from  the  test, 
intensely  green,  or  light  green  if  lead  predominates, 
with  a  yellow  seam  inside.  On  cooling  it  changes  very 
little> 

Antimony. — It  covers  the  charcoal  with  a  white  oxyd 
or  bluish  white  if  in  a  thin  layer.  The  coating  is  not 
close  to  the  assay  and  is  easily  driven  away.  If  a  great 
deal  of  silver  be  present,  the  coating  appears  pink. 

Zinc. — The  coating  of  the  oxyd  of  zinc  is  near  to  the 
test,  appears  yellow  when  hot,  and  turns  white  on  cool- 
ing. Heated  with  the  oxydation  flame,  the  coating 
becomes  luminous. 

Tin. — The  coating  is  quite  close  to  the  test.    It  is 
yellow  when  hot  and  white  when  cold,  resembling  the 
coating  of  zinc.  Becomes  also  luminous.  In  the  reduc- 
2 


18  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

tion  flame  the  coating  of  oxyd  can  be  reduced  to  the 
metallic  state. 

Selenium — Gives  a  steel  gray  coating  of  a  feeble  metal- 
lic lustre,  showing  somewhat  violet  color  further  off; 
played  upon  with  the  flame,  it  emits  a  rotten  radish-like 
odor. 

Tellurium. — It  fumes  and  coats  the  coal  white  with  a 
red  or  dark  yellow  seam. 

Examining  ore  on  charcoal,  it  cannot  be  expected  to 
get  always  coatings  which  agree  exactly  with  the  de- 
scription, there  being  generally  different  metals  present. 
If,  for  instance,  the  ore  under  examination  contains  lead, 
zinc,  and  antimony,  the  white  coating  with  a  blueish 
seam  will  appear  first,  and  is  recognized  as  antimony. 
But  it  soon  becomes  yellow  from  the  oxyd  of  lead, 
which,  mixed  with  the  white  antimony  coating  appears 
lighter.  The  zinc  coating  which  is  also  yellow  colored 
is  not  distinguishable  at  first  from  the  lead  coating,  but 
this  latter  can  be  blown  away  with  the  oxydation  flame, 
leaving  the  zinc  oxyd,  which  appears  luminous  when 
played  upon  with  the  oxydation  flame. 

EXAMINATION  WITH  BORAX  AND  SODA, 
On  Charcoal. 

Sec  7.  The  borax  assumes  a  globular  shape  when 
melted  on  charcoal  with  the  blowpipe.    If  pure,  it  ap- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  19 

pears  colorless,  and  dissolves  the  oxyds  of  metals.  If 
sulphurets  are  taken  in  examination,  they  must  be  pow- 
dered and  a  small  portion  of  it  treated  with  the  reduction 
flame,  on  charcoal,  in  order  to  drive  out  the  sulphur 
and  arsenic.  If  the  sulphurets  melt,  the  powder  may 
be  mixed  with  charcoal  dust  and  treated  to  a  dark  red 
heat.  A  very  small  part  of  this  roasted  ore,  or  not 
roasted  if  the  test  consists  of  oxyds,  is  put  on  the  borax 
pearl,  and  melted  with  the  oxydation  flame.  If  the  color 
of  the  glass  is  not  perceptibly  changed,  another  particle 
of  the  ore  can  be  dissolved,  but  it  is  never  advisable  to 
take  too  much  in  the  first  instance.  If  the  globule  be 
too  dark  in  color,  it  may  be  flattened  by  a  pair  of  pin- 
cers after  blowing,  before  getting  stiff,  and  then  observ- 
ed against  the  light. 

A  colored  borax  glass  appears  often  different  when 
cold  or  warm,  also  if  treated  with  the  outer  or  inner 
flame ;  there  are,  however,  but  a  few  metals  to  be  con- 
sidered for  our  purpose. 

Iron. — It  colors  the  borax  reddish  yellow  or  reddish 
brown,  when  hot  and  played  upon  with  the  oxydation 
flame.  It  turns  yellow,  or  colorless  if  in  a  small  quan- 
tity, when  cold.  A  good  reduction  flame  makes  the 
glass  reddish  brown,  but  it  becomes  bottle  green  when 
cold. 

Copper — When  hot,  colors  the  glass  green ;  when 
cold,  blue.    The  presence  of  other  metals  renders  these 


20  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

signs  uncertain.  The  surest  way  is,  to  reduce  the  oxyd 
of  copper  which  is  dissolved  in  the  borax,  to  a  suboxyd 
by  which  the  glass  assumes  a  light  red  color,  becoming 
opaque. 

When  the  well-calcined  test  is  dissolved  in  borax,  a 
small  piece  of  tinfoil  is  laid  on  the  pearl  and  blown  with 
the  reduction  flame.  If  there  is  only  a  small  quantity 
of  copper  in  the  ore.  the  borax  pearl  will  appear  brick 
red  and  opaque  when  cold.  If  the  color  is  grayish 
brown,  there  is  also  some  antimony  in  the  test.  If  the 
pearl  becomes  black  there  is  a  great  deal  of  antimony, 
which  must  be  driven  off  by  a  better  roasting. 

EXAMINATION  IN  A  CLOSED  GLASS  TUBE. 

Sec.  8.  A  particle  of  ore,  of  the  size  as  represented  in 
Fig.  7  tf,  is  introduced  into  a  glass  tube  (Fig.  7  b)  and 
heated  by  an  alcohol  lamp.  The  heat  must  be  raised 
gradually  to  redness,  also  increased,  if  no  sublimate 
appears,  directing  the  alcohol  flame  by  the  blowpipe 
on  that  part  of  the  tube  where  the  particle  of  ore  is,  till 
the  glass  commences  to  melt. 

The  volatile  substances  sublimate  on  the  cooler  part 
of  the  tube  (Fig.  7  c),  assuming  different  colors,  thus 
enabling  us  to  recognize  the  substance. 

a.  A  dark  yellow  or  reddish-brown  sublimate  when 
hot,  turning  the  sulphur  yellow  when  cold,  indicates 
sulphur.    Only  such  sulphurets  which  contain  two  atoms 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  21 

of  sulphur  to  one  atom  of  metal  emit  sulphur  in  a  closed 
tube. 

b.  A  reddish  yellow  sublimate  which  appears  at  a  high 
temperature  under  the  blowpipe,  becoming  sulphur  yel- 
low when  cold,  shows  iodine. 

c.  A  dark  reddish-brown,  almost  black  sublimate, 
becoming  red  or  reddish-yellow  after  cooling,  shows  the 
presence  of  arsenic  and  sulphur. 

d.  A  black  sublimate,  quite  close  to  the  test,  arising 
by  the  aid  of  the  blowpipe  and  turning  brownish-red 
when  cold,  indicates  sulphur  and  antimony. 

c.  A  black  sublimate  without  lustre,  rendering  a  red 
powder  when  scratched,  indicates  sulphur  and  mercury. 

/.  A  grayish-white  sublimate,  consisting  of  trans- 
parent crystals,  which  can  be  distinguished  under  the 
magnifying  glass,  indicates  antimony.  Some  ore  will 
not  yield  this  sublimate,  unless  it  is  treated  with  the 
blowpipe. 

g.  A  reddish  black  sublimate,  obtained  by  the  aid  of 
the  blowpipe,  giving  a  dark  red  powder,  indicates  selen- 
ium, which  can  be  observed  at  the  open  end,  by  the 
odor  of  rotten  radish. 

h.  A  gray  sublimate  indicates  mercury.  The.  quick- 
silver globules  can  be  perceived  by  a  magnifying  glass. 


22 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


EXAMINATION  IN  A  GLASS  TUBE, 
Open  at  Both  Ends. 

Sec.  9.  For  the  purpose  of  examining  the  ore  in  an 
open  tube,  the  test  is  introduced  so  as  to  have  it  near 
one  end.  That  part  of  the  tube  is  heated  over  the 
alcohol  flame,  while  the  other  end  is  raised  a  little,  so 
as  to  create  a  draft.  It  is  often  required  to  raise  the 
heat  by  aid  of  the  blowpipe,  as  described  in  Section  8. 
The  ore  is  used  in  shape  of  grain,  about  as  large  as 
hempseed  ;  but,  if  it  was  observed  to  decrepitate  in  the 
closed  tube,  it  must  be  pulverized,  and  in  that  state 
introduced  into  the  tube. 

There  are  substances  or  combinations,  which  are  not 
volatile  in  a  closed  tube,  but  being  in  contact  with  the 
oxygen  of  a  draft  of  air  in  an  open  tube,  they  oxydize 
and  escape,  either  in  form  of  gas,  when  they  can  be  per- 
ceived by  their  odor,  or  by  their  action  on  a  strip  of 
moistened  blue  litmus  paper,  which  is  placed  in  the 
upper  part  of  the  tube,  or  they  sublime  in  the  cooler 
part,  nearer  to  the  test,  or  further  off,  according  to  the 
degree  of  their  volatility. 

Care  must  be  taken  to  raise  the  heat  gradually, 
otherwise  it  may  happen  that  a  great  part  of  the  sub- 
stance will  sublime  without  change.  There  are  several 
substances,  which,  treated  in  an  open  tube,  can  be  recog- 
nized with  certainty.    Such  substances  are  principally : 

Sulphur. — Sulphurets,  being  heated  in  a  tube,  emit 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  23 

sulphurous  acid.  The  sulphur  can  be  detected  by  the 
odor  at  the  upper  end  of  the  tube,  also  by  the  litmus 
paper,  which  changes  its  blue  color  into  red. 

Antimony. — Antimony  yields  white  fumes,  condensing 
in  the  upper  part  of  the  tube  to  a  white  sublimate.  The 
presence  of  lead  makes  the  sublimate  light  yellow. 

Selenium. — Selenium  of  silver  emits  at  the  upper  end 
of  the  tube  the  odor  of  rotten  radish. 

Iodine. — Iodide  of  silver,  if  strong  heat  is  applied, 
gives  a  yellow  sublimate.  .  It  changes  sulphur  yellow 
when  cold. 

Quicksilver.— Quicksilver  gives  a  sublimate  of  metallic 
mercury  of  a  grayish-white  appearance.  If  sulphur  is 
present  and  strong  heat  is  applied,  a  black  coating  will 
be  formed. 

SYSTEMATIC  PROCEEDING 
For  Determination  of  Gold  and  Silver  Ores. 

Sec.  10.  The  use  of  the  following  systematic  proceed- 
ing can  be  understood  easily  by  an  example  : 

A  silver  mineral,  for  instance,  approved  as  such  by 
examination  on  silver,  must  be  observed  first  as  to  what 
lustre  it  shows,  or  whether  it  is  dull.  Suppose,  then  the 
mineral  has  a  metallic  lustre  (see  I).    The  color  must 


24 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


be  observed  next  and  compared  with  those  under  I. 
The  ore  is  further  found  to  be  "  lead  gray."  We  have 
then  to  proceed  from  the  indicated  letter  B  on  the 
right  side  to  B  on  the  left,  and  examine  accordingly, 
whether  the  mineral  gives  a  sublimate  or  not.  If,  for 
instance,  no  sublimate  has  been  obtained,  we  must  pro- 
ceed to  c  as  indicated.  On  the  described  examination 
under  c  the  mineral  appears  tough,  it  can  be  cut  with  a 
knife.  We  go  over  to  Section  16,  and  see  the  numbers 
2  and  20,  Silverglance  and  Hessite.  The  description 
of  both  will  lead  to  the  right  determination  of  the 
mineral. 


I.  LUSTRE-METALLIC  OR  SUB-METALLIC . 

Color — white,  grayish  white,  yellowish  white,  or  yellow,  see. .  .  A 

Color — lead-gray,  blackish  lead-gray,  or  iron-black   B 

Color — light  steel-gray   C 

Color — reddish  lead-gray   D 

Color — pinchbeck  brown.   E 

II.  LUSTRE-RESINOUS  AND  ADAMANTINE. 

Color — pearl-gray,  yellowish  green,  green,  olive-green,  lemon 

yellow  or  light  yellow,  see   F 

III.  DULL. 

Color — red,  dark  red  (sometimes  externally  lead-gray),  see.  . .  67 

Color — blackish  blue   H 

Color — greenish  black   I 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  25 

A  It  can  be  cut  with  a  lgiife,  see   a 

A  Can  not  be  cut,  is  brittle   b 

B  In  a  closed  tube,  no  sublimate,  even  under  the  blowpipe ....  e 

B  It  gives  a  sublimate,  with  or  without  the  blowpipe   d 

0  In  a  closed  tube,  no  sublimate   e 

C  It  gives  a  sublimate   / 

Z>  In  a  closed  tube,  dark  red,  sublimate.    See  Sec.  16  (8  or  9). 

E  In  a  closed  or  open  tube,  no  sublimate.    Sec.  16  (4). 

F  In  a  closed  or  open  tube,  no  sublimate   g 

F  Gives,  with  aid  of  the  blowpipe,  a  slight  sublimate   h 


G  In  a  closed  tube,  red-brown  or  reddish  yellow  sublimate. 
Sec.  16  (10). 

G  It  gives  three  sublimates,  black,  yellow,  and  gray.    Sec.  16 
(16). 

S  In  an  open  or  closed  tube,  no  sublimate.    Sec.  16  (3  #'). 
I  In  an  open  or  closed  tube,  no  sublimate.    Sec.  16  (11  a'). 
a    It  melts  on  charcoal  to  a  metallic  white  globule.    Sec.  16  (1). 
a    It  melts  on  charcoal  to  a  metallic  yellow  or  yellowish  globule. 
Sec.  15  (1). 

b    It  melts  on  charcoal  to  a  globule  of  metallic  lustre,  coating  the 

coal  white.    Sec.  16  (17). 
b    It  decrepitates  somewhat,  giving,  before  fusing,  a  slight,  very 

volatile  whitish  coating.    Sec.  15  (4)  or  Sec.  16  (22  or  23). 
c    It  can  be  cut  with  a  knife.    Sec.  16  (2  or  20). 
c    It  can  not  be  cut,  is  brittle.    Sec.  16  (3  or  4,  a  or  6),  or  Sec. 

15  (2). 

d  In  a  closed  tube  it  gives  a  reddish  yellow  sublimate.    Sec.  16 
(6  «'). 

e    On  charcoal  it  fuses,  giving  a  yellow  and  white  coating.  Sec. 
15  (3). 

/    In  a  closed  tube,  by  aid  of  the  blowpipe,  a  dark  red  sublimate. 
Sec.  16  (11). 


26  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

g    On  charcoal  it  fuses,  emits  an  acrid  odor,  and  leaves  globules  of 
silver  ;  in  a  closed  tube  with  bisulphate  of  potassa,  emits  no 
colored  vapors.    Sec.  16  (12). 
g    It  gives,  with  bisulphate  of  potassa,  red-brown  vapors.  Sec. 
16  (13  or  14). 

h    In  a  closed  tube,  with  bisulphate  of  potassa,  violet  vapors. 
Sec.  16  (15). 

ANALYSIS  OF  RETORTED  AMALGAM, 
Or  Bullion  Metal. 

Sec.  11.  Black  amalgam  is  first  tried  with  the  magnet 
on  a  small  particle.  If  attracted,  there  is  a  great  deal 
of  iron  in  the  amalgam.  If  it  does  not  follow  the  mag- 
net, it  may  still  contain  iron,  which  must  be  examined 
in  a  different  way. 

A  small  piece  is  introduced  into  a  closed  tube  and 
heated  by  the  alcohol  lamp  to  redness.  It  generally 
gives  out  a  whitish  sublimate,  consisting  of  minute  glob- 
ules of  mercury,  which  can  be  detected  by  the  magnify- 
ing glass,  or  by  a  piece  of  flattened  gold,  which,  when 
introduced  into  the  tube  and  rolled  over  in  the  sublimate, 
gets  a  coating  of  quicksilver. 

Heated  in  an  open  tube,  it  sometimes  colors  litmus 
paper  red.  This  proves  the  presence  of  sulphurets  in 
the  amalgam.  Under  such  circumstances  a  black  subli- 
mate appears,  consisting  of  sulphur  and  mercury. 

A  small  particle  of  bullion  metal  or  retorted  amalgam 
is  laid  on  charcoal  and  heated  with  the  oxydation  flame. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  27 

A  slight  yellow  coating  indicates  lead ;  a  bluish-white, 
antimony ;  or  the  coating  is  yellowish,  and  further  off 
bluish  white,  proving  the  presence  of  both  lead  and  an- 
timony. 

On  a  clean  spot  of  the  charcoal,  some  borax  is  melted 
into  a  transparent  globule.  The  metal  is  placed  against 
the  borax  and  played  upon  with  the  reduction  flame  for 
half  a  minute.  The  oxydation  flame  would  oxydize  the 
silver,  and  color  the  pearl  white  enamel-like  in  cooling. 
The  metal  globule,  when  yet  hot,  is  seized  by  a  pair  of 
pincers  and  taken  out,  leaving  the  borax  pearl  on  the 
coal.  To  this  pearl  is  added  some  tinfoil  of  the  size  of 
a  small  pinhead,  and  blown  again  only  a  short  time  with 
the  reduction  flame.  If  the  pearl  turns  gray  enamel-like 
or  black,  it  shows  the  presence  of  antimony,  which,  on 
account  of  its  small  amount,  could  not  have  been  per- 
ceived as  a  coating  on  the  charcoal.  In  this  case  another 
small  particle  of  the  same  test  must  be  played  upon  with 
the  pure  oxydation  flame  for  about  one  minute,  in  order 
to  get  rid  of  the  antimony,  and  then  treated  with  borax 
and  tinfoil  as  above  described.  If  there  be  copper  in 
the  metal,  the  glass  would  appear  brick-red  or  dark 
brown  when  cold  under  the  influence  of  the  tinfoil. 

The  same  pearl  is  played  upon  again  with  a  good 
reduction  flame  for  half  a  minute  in  order  to  reduce  the 
copper  to  a  metallic  condition.  If  then,  the  glass  appears 
transparent  greenish  or  bottle  green,  there  is  iron  pres- 
ent in  the  metal.  If  it  does  not  become  transparent,  a 
longer  blowing  or  better  reduction  flame  is  required. 


28 


PROCESSES  OF  SILVER  AXD  GOLD  EXTRACTION. 


BLOW-PIPE  ASSAY. 

Sec.  12.  For  the  purpose  of  determining  a  silver  min- 
eral, it  is  not  absolutely  necessary  to  ascertain  the 
amount  of  silver  or  the  specific  gravity.  In  some  cases, 
however,  it  may  be  desirable  to  know  both.  To  ascer- 
tain the  silver  by  fire  assay,  would  not  answer ;  firstly, 
because  there  are  generally  different  silver  minerals  in 
the  ore,  the  separation  of  which  in  the  required  quantity 
would  be  almost  impossible,  and  because  the  fire  assay 
is  not  accurate  enough  for  this  purpose. 

In  analyzing  silver  ore  it  is  important  to  examine  it 
with  the  magnifying  glass,  and  to  select  pieces  which 
are  of  the  same  quality  in  regard  to  toughness,  color, 
lustre,  and  fracture.  A  preliminary  examination  with 
the  blow-pipe  will  inform  us  of  the  compound,  and  enable 
us  to  know  whether  the  different  pieces  are  substantially 
the  same.  Rich  silver  ore  should  be  examined  carefully 
with  the  aid  of  a  magnifying  glass,  and  the  small  par- 
ticles of  native  silver  adhering  to  the  mineral  removed 
by  a  pair  of  pincers.  This  precaution  must  be  observed, 
likewise,  in  selecting  pieces  for  the  determination  of  spe- 
cific gravity. 

One  grain  of  the  silver  mineral  is  sufficient  for  the 
blowpipe  assay,  and,  if  properly  conducted,  will  always 
yield  the  same  amount  of  silver,  as  found  in  the  classifi- 
cation, provided  it  is  a  mineral  with  an  invariable  amount 
of  silver,  for  instance  silverglance. 

For  the  purpose  of  assaying,  the  mineral  must  be  pul- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  29 


verized  in  the  agate  mortar  to  the  finest  powder.  Tough 
silver  ore  can  be  used  in  little  pieces.  Of  this  prepared 
ore,  1  grain  or  yVW  is  weighed  out  on  the  assay  balance 
(see  Sec.  3)  with  the  utmost  precision,  and  emptied  into 
the  mixing  scoop  (see  Fig.  3).  Some  powder  always 
remains  in  the  balance  cup  which  must  be  swept  with  a 
little  hair  brush  into  the  capsule.    (Fig.  3.) 

The  required  quantity  of  borax  glass  and  lead  (Sec.  4) 
depends  on  the  ore.  About  T££o  °f  borax  will  generally 
answer,  but  if  the  test  appears  difficult  to  be  melted, 
some  more  borax  may  be  added  during  the  smelting 
operation.  Three  times  as  much  lead  as  silver  ore 
should  be  used.  If  there  is  a  great  deal  of  copper  in 
the  mineral,  a  double  quantity  of  lead  is  required. 

The  ore,  lead,  and  borax  are  mixed  carefully  in  the 
capsule  with  an  iron  spatula.  When  this  is  done,  the 
spatula  is  brushed  above  the  capsule  and  the  mixture 
introduced  into  the  paper  tube  (Sec.  3).  To  effect  this, 
the  paper  tube  is  gently  held  between  the  thumb  and 
forefinger.  The  capsule  is  held  with  the  thumb  and  fore- 
finger of  the  right  hand,  and  the  mouth  of  the  capsule 
introduced  so  far  into  the  tube  that  it  can  be  held, 
together  with  the  tube,  by  the  left  hand. 

The  assay  slides  into  the  tube  by  gently  knocking 
with  the  spatula  upon  the  capsule.  The  remaining  dust 
must  be  swept  into  the  tube  with  the  hair  brush.  The 
tube  is  then  closed,  folding  the  paper  with  the  fingers, 
and  is  thus  prepared  for  melting. 

For  this  purpose,  a  hole  is  made  in  a  sound  piece  of 


30  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

charcoal  with  the  little  drill  (Fig.  2)  deep  enough  to 
receive  the  prepared  tube,  which  is  introduced.  The 
hole  must  be  always  made  across  the  grain  of  the  coal 
near  the  edge.  The  reduction  flame  is  now  conducted 
so  as  to  cover  the  tube  by  easy  blowing.  A  strong  blast 
would  carry  off  the  paper  which  was  folded,  and  cause 
some  loss.  When  the  tube  paper  is  burned  and  the 
assay  commences  to  melt,  a  strong  heat  must  be  applied 
with  a  pure  reduction  flame  which  is  chiefly  turned 
upon  the  borax,  not  upon  the  lead  button.  The  latter 
gains  in  size  by  the  joining  of  other  globules.  When 
the  melting  has  proceeded  so  far  that  only  slag  and  the 
lead  button  are  perceived,  the  blowing  must  be  inter- 
rupted, in  order  to  bring  the  bottom  of  the  tube,  which 
may  be  yet  under  the  slag,  to  the  top,  by  tapping  the 
coal  with  the  finger.  The  application  of  the  reduction 
flame  is  continued  till  no  particles  of  lead  are  seen  on 
the  slag.  The  charcoal  must  be  inclined  in  different 
directions,  so  that  the  lead  button  may  touch  all  sides 
of  the  slag,  gathering  up  the  small  lead  globules.  When 
this  is  performed,  the  oxydation  flame  must  be  used, 
chiefly  for  the  purpose  of  driving  out  the  sulphur.  The 
assay  must  be  kept  as  far  from  the  flame  as  possible. 

The  blast  is  directed  right  on  the  lead  button.  It 
will  soon  be  perceived,  that  many  little  lead  globules 
arise  in  the  slag,  but  they  do  not  contain  silver.  The 
lead  oxyd,  produced  by  the  oxydation  flame,  is  dissolved 
by  the  borax,  and,  in  contact  with  the  glowing  coal, 
reduced  to  the  metallic  state.    After  a  time  the  melting 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  31 

is  interrupted,  and  when  it  is  observed  that  the  lead 
button  turns  black  on  cooling,  the  blowing  must  be  con- 
tinued for  half  a  minute  more.  If  the  lead,  when  hard- 
ened, has  a  light  lead-color  it  may  be  broken  out,  with 
a  pair  of  pincers,  and  cleaned  of  slag  on  the  anvil  with 
the  little  hammer. 

The  button  is  now  ready  for  cupellation.  The  bone- 
ash  cupel  (Fig.  4,  b)  is  heated  in  the  oxydation  flame, 
and  the  lead  button  introduced.  The  object  of  this 
operation  is  the  oxydation  of  the  lead,  which  is  thereby 
separated  from  silver.  The  lead  button  in  the  cupel  is 
played  upon  with  the  oxydation  flame,  using  a  strong 
heat.  As  soon  as  the  lead  becomes  bright  and  active 
the  cupel  is  held  a  little  further  off  from  the  flame  and 
a  moderate  heat  is  applied,  but  not  so  low  as  to  stop  the 
action.  The  flame  must  be  directed  on  the  lead.  The 
litharge  accumulates  behind  the  button,  which,  when 
reduced  to  the  size  as  represented  by  c  (Fig.  4),  must 
be  separated  from  the  litharge,  by  using  more  heat  on 
and  around  the  button,  holding  at  the  same  time  the 
capul  a  little  inclined,  so  that  the  globule  may  slide  off 
on  a  clean  spot.  The  cupel  is  held  nearer  to  the  flame, 
which  must  play  around  the  button,  in  order  to  heat  the 
cupel,  by  which  the  litharge  as  it  is  formed  sinks  into 
the  mass,  leaving  finally  a  pure  silver  globule.  When 
the  last  particles  of  litharge  are  emitted,  the  globule 
assumes  the  color  of  the  rainbow,  which  indicates  the 
finishing  operation  requiring  a  few  seconds  mare  blow- 
ing.   If  there  was  too  much  copper  in  the  assay,  the 


32  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

silver  button  will  appear  dark  or  black.  An  addition  of 
lead  of  the  size  of  a  pin-head,  and  treated  again  with  the 
blowpipe  for  a  moment  will  render  the  button  bright. 

The  silver  button  is  taken  from  the  cupel,  laid  edge- 
ways on  the  anvil  and  the  adhering  boneash  hammered 
off.  It  is  then  weighed  on  the  balance  and  the  per  cent- 
age  is  found  directly  by  noticing  the  weight. 

If  required  to  express  the  per  centage  in  ounces  per 
ton,  it  may  be  calculated  in  the  following  way  :  for 
instance,  one  hundred  parts  of  silver  ore  assayed  in  the 
described  way,  yielded  a  button,  weighing  sixty-three. 
This  mineral  contains,  then,  sixty-three  per  cent,  of  sil- 
ver, consequently  twenty  times  so  much  per  ton  of 
2,000  lbs.,  of  which  one  pound  contains  14*58  ounces 
Troy.    The  calculation  accordingly  is : 

63  X  20  =  1260  X  14*58  =  18,370-80  ounces  per  ton. 

The  silver  button,  when  dissolved  in  nitric  acid, 
leaves  sometimes  a  black  particle  of  gold,  which  is 
always  insignificant  and  without  influence  in  classifica- 
tion. 

The  application  of  too  much  heat  in  cupellation  may 
cause  a  serious  loss  of  silver.  It  is  therefore  necessary 
to  keep  the  cupel  sufficiently  far  off  from  the  flame  and 
allow  the  litharge  to  become  stiff,  as  soon  as  it  parted 
from  the  metal.  But  also  in  this  case  a  certain  loss 
must  be  suffered,  which,  as  found  by  experience,  must 
be  added  to  the  weight  of  the  button. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  33 


The  following  extract  from  Plattner's  Table  of  Silver 
Losses  by  Cupellation  will  serve  our  purpose : 


If  the  silver  button 
weighed  : 

Ores  containing  30  to  59  per 
cent,  of  copper,  required  11 
parts  of  lead  to  1  part  of 
ore. 

Ores  containing  under  7  per 
cent,  of  copper,  or  free  from 
it,  require  5  parts  of  lead  to 
1  of  ore. 

The  loss  of  silver  in  cupellation  will  be  : 

80 

  0-44 

70 

  0-82 

  0'40 

60  

  0-74 

  0-36 

50 

  0-56 

  0  32 

A  ft 

  0-55 

  0  27 

30  

  0-50 

  0-25 

20  

  0-45 

  0  22 

10  

  0  40 

  0  20 

!'^~9  

  0  35 

  0-17 

8  

  0-28 

7  

  0  23 

  0-13 

6  

  0-20 

  0-11 

5  

  0-18 

  040 

4  

  0-16 

  0-09 

According  to  this  table  the  real  amount  of  silver  in  the 
supposed  assay  of  the  silver  ore  (which,  in  the  absence 
of  copper  was  mixed  with  5  parts  of  lead)  must  be 
.equal  to  63  -|-  0-37  =  63-37  per  cent. 


SPECIFIC  GRAVITY. 

Sec.  13.  The  determination  of  specific  gravity,  for 
the  purpose  of  the  classification  of  silver  ore  is  not  abso- 
lutely necessary,  but  in  some  cases  it  may  be  of  service. 

The  specific  gravity  of  a  mineral  is  its  weight,  com- 
pared with  the  weight  of  an  equal  body  of  distilled  or 
pure  water. 

3 


34 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


It  is  necessary  to  know  the  absolute  weight  of  the 
mineral;  then  that  of  an  equal  volume  of  water,  and  to 
divide  the  first  by  the  last.  The  mineral  by  immersion 
loses  exactly  so  much  in  weight  as  an  equal  bulk  of 
water  weighs.  The  loss  of  weight  of  a  mineral  by 
immersion  expresses,  therefore,  the  weight  of  an  equal 
volume  of  water.  If  the  absolute  weight  of  a  mineral 
is  divided  by  its  loss  under  water,  the  quotient  will  show 
the  specific  gravity. 

For  instance,  a  piece  of  native  gold  (Comstock)  weighs   183*8 

The  same  piece  under  water   170*8 

Difference   13*0 

183*8 

The  difference,  13,  is  the  loss  of  weight  by  immersion,  and  =  14*1  spe- 
cific gravity  of  gold. 

The  blowpipe-balances  are  provided  for  hydrostatic 
weighings,  as  represented  by  Fig.  8.  On  the  little  hook 
of  the  scale,  a,  is  fastened  a  fine  silk  thread  prepared 
with  a  sling  (for  the  mineral,  whicn  may  weigh  two  or 
three  grains).  The  scales  are  set  to  balance,  including 
the  thread.  The  mineral  is  then  suspended  on  the 
thread,  weighed,  and  the  weight  noticed.  A  small  tum- 
bler, c,  is  placed  under  the  scale,  a,  and  the  suspended 
mineral,  by  immersed  about  one-fourth  of  an  inch  below 
the  surface  of  the  water.  If  any  bubbles  are  perceived 
on  the  mineral,  they  must  be  removed  by  the  aid  of  a 
small  hair  brush.  It  is  weighed  again  now,  and  the  loss 
by  immersion  found. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


35 


HARDNESS. 

Sec.  14.  In  regard  to  gold  and  silver  ores,  the  hard- 
ness is  not  very  important,  inasmuch  as  there  is  no  con- 
siderable variation  among  these  minerals.  Chapman's 
arrangement,  by  which  the  hardness  can  be  ascertained 
without  the  use  of  minerals,  representing  the  scale  of 
hardness,  will  sufficiently  answer  our  purpose. 

Hardness  =  1*5  yields  with  difficulty  to  the  nail. 

Hardness  —  2-5  does  not  yield  to  the  nail ;  does  not  scratch  a  copper  coin, 
but  is  easily  scratched  by  it. 

Hardness  =  3*5  scratches  a  copper  coin  easily,  but  is  scratched  by  it  with 
difficulty. 


CHAPTER  II. 


DESCRIPTION  OF  GOLD  AND  SILVER  ORES. 

A.    GOLD  ORES. 

Sec.  15.  Gold  appears  mostly  in  metallic  condition, 
but  never  free  from  silver.  It  is  found  generally  in  the 
form  of  grains,  scales,  dust,  also  in  the  shape  of  leaves, 
threads  or  crystals.  It  is  not  ascertained  but  supposed, 
that  a  part  of  the  gold  in  iron  pyrites  does  not  exist  in 
metallic  state,  but  combined  with  sulphur,  or  with  arsenic 
in  the  arsenical  pyrites.  The  gold  is  found  in  combina- 
tion with  the  following  metals : 

1.  Silver — In  different  proportions.  The  gold  of  Gold 
Hill  lode,  N.  T.,  contains  forty-seven  to  fifty  per  cent,  of 
silver ;  that  of  the  Comstock  lode  thirty  to  forty-five. 
Gila  River  and  Australian  gold  three  to  five  per  cent., 
according  to  the  amount  of  silver  the  gold  appears 
more  or  less  whitish.  Sixty  per  cent,  of  silver  renders 
the  alloy  white. 

On  charcoal,  treated  with  the  oxydation  flame,  it  gives 
sometimes  a  bluish-white  coating  of  antimony.  With 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


37 


borax,  played  upon  with  reduction  flame,  a  reaction  of 
copper  may  be  observed. 

2.  With  Tellurium. — It  contains  gold  26,  silver  14, 
tellurium  59,  with  traces  of  lead,  copper,  and  antimony, 
hardness  1-5,  gravity,  5*7  to  5*8,  lustre  metallic,  color 
light  gray. 

In  an  open  tube  it  emits  white  fumes,  and  gives  a 
gray  sublimate  of  tellurium.  Directing  the  flame  on 
the  sublimate,  it  melts  into  transparent  drops.  The 
fumes  have  a  peculiar  sour  odor.  On  charcoal  it  melts 
to  a  dark  gray  globule.  Played  upon  with  the  oxyda- 
dation  flame  it  gives  a  white  coating,  which  disappears 
with  a  bluish-green  color  under  the  oxydation  flame. 
Continued  blowing  yields  a  yellow,  bright  gold  button. 

3.  With  Tellurium  and  Lead. —  Gold  9,  tellurium  32, 
lead  54,  with  traces  of  copper,  sulphur,  and  antimony ; 
H.  =  1-5,  Gr.  ==  7-7*2,  color  dark  lead-gray. 

In  an  open  tube  it  fumes,  and  yields  a  gray  sublimate, 
the  upper  part  of  which,  formed  by  antimonous  acid, 
can  be  driven  away  by  the  flame.  On  charcoal  it  fumes 
and  gives  two  coatings :  a  white  one,  which  is  volatile, 
consisting  of  tellurous  and  antimonous  acids  and  sul- 
phate of  lead j  the  other  coating  is  yellow,  less  volatile, 
and  consists  principally  of  oxyd  of  lead.  Continued 
blowing  leaves  a  small  metallic  button,  showing  gold 
color  when  cupeled. 

4.  With  Mercury  and  Silver. — Gold  36,  silver  5,  mer- 


38  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


cury  58.  The  gold  is  found  also  alloyed  with  molyb- 
denum, platinum,  and  rhodium. 

B.    SILVER  ORES. 

Sec.  16.  Silver  is  found  mostly  in  combination  with 
sulphur,  also  alloyed  with  other  metals  and  substances. 
It  appears  often  in  metallic  condition. 

1.  Native  Silver — Is  found  crystalized,  in  threads  or 
filaments.  It  often  contains  a  small  amount  of  anti- 
mony, arsenic,  iron,  gold,  or  copper.  The  native  silver 
(one  variety)  of  the  Comstock  lode,  N.  T.,  contains  :  Sil- 
ver 60-85,  gold  1-9,  lead  8-30,  copper  1-5,  H.=  2-7 
-3,  Gr.  =  10-6-11-3.  Heated  on  charcoal  it  becomes 
covered  with  lead  globules,  disappearing  again  when 
red  hot.  It  gives  a  yellow  coating  of  lead,  and  further 
off  a  bluish-white  of  antimonous  acid.  It  colors  the 
borax  glass  green  with  the  oxyd  of  copper. 

a.  Combination  with  Sulphur. 

2.  Silver  Glance  (Sulphuret  of  Silver). — Silver  87, 
sulphur  12'9,  H.^2-5,  Gr.  =  6- 9-7*2,  lustre  metallic, 
color  and  streak  blackish  lead-gray,  streak  shining.  It 
may  be  cut  like  lead.  On  charcoal,  it  melts  into  a  dark 
blue  globule,  generally  emitting  metallic  silver  on  the 
surface  on  cooling,  especially  if  a  small  particle  of  borax 
glass  is  added,  which  dissolves  impurities.  It  yields  a 
silver  globule  when  melted  with  soda. 


♦ 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  39 


3.  Stromeyerite  (Silver-copper  Glance). — Silver  50-53, 
copper  31,  sulphur  15,  H.  =  2*5,  Gr.  =  6-2,  lustre  metallic, 
color  blackish  lead-gray.  In  a  closed  tube  gives  some- 
times a  little  sulphur  sublimate,  in  an  open  tube  sulphur- 
ous acid.  On  charcoal  it  fuses  to  a  steel  blue  globule, 
emitting  sometimes  metallic  silver  on  cooling.  Melted 
with  soda,  it  gives  a  copper  button,  which  yields  silver 
when  refined.  It  occurs  in  the  Heintzelman  mine  (Ari- 
zona). 

a\  A  variety  of  this  ore,  containing  40-43  per  cent, 
of  silver  with  a  dull  blackish-blue  color,  streak  shining, 
can  be  cut,  occurs  in  Arizona. 

4.  Sternbergite  (Sulphuret  of  Silver  and  Iron). — Silver 
30-33,  iron  36,  sulphur  30,  H.  =  1,  Gr.  =  4-2,  me- 
metallic  lustre,  color  pinchbeck-brown,  streak  black.  In 
thin  laminae  flexible,  resembling  graphite.  In  an  open 
tube  it  gives  out  sulphurous  acid.  It  melts  to  a  globule 
on  charcoal,  emitting  silver,  and  follows  the  magnet. 

a\  A  variety  of  this  ore  is  found  in  the  Gold  Hill  lode, 
N.  T.  It  consists  of  silver  33-25,  iron  34-05,  H.  =  2-8, 
Gr.  =  5-2,  color  dull  bluish-gray  ;  the  fracture  has  a 
metallic  lustre  and  dark  lead-gray  color.  The  powder 
is  blackish-brown.  It  is  found  in  small  fragments  of 
indistinct  cubic  shape.  On  charcoal  it  melts  with  a 
spongy  appearance  to  a  dull  gray  globule,  following  the 
magnet.  A  slight  yellow  coating  indicates  a  trace  of 
lead.  In  melting  it  gives  out  a  great  deal  of  sulphur- 
ous acid.  Treated  with  soda  a  silver  globule  is  easily 
obtained. 


40 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


b.  Combinations  with  Sulphur  and  Antimony,  or  Arsenic. 

5.  Brittle  Silver  Ore. — Silver  70,  antimony  13*9,  sul- 
phur 15*7,  H.  =  2*5,  Gr.  =  6-2,  lustre  metallic,  color  and 
streak  iron  black  or  blackish  lead-gray.  In  a  close  tube 
it  decrepitates,  melts  to  a  globule  and  gives  a  blackish 
sublimate  which  turns  red-brown  when  cold,  consisting 
of  sulphide  of  antimony.  In  an  open  tube  it  melts, 
evolving  sulphurous  acid,  and  fumes.  On  charcoal  it 
fuses,  and  coats  the  coal  white  with  antimonous  acid. 
By  continual  blast,  the  coating  assumes  a  pink  color, 
derived  from  the  oxyd  of  silver.  It  occurs  frequently 
in  the  Comstock  lode. 

7 

6.  Polylasite  (Eugen  Glance). — Silver  64-72,  copper 
3-10,  sulphur  17,  H.  =  2*5,  Gr.  =  6-2.  It  contains  also 
antimony,  arsenic,  iron,  and  sometimes  zinc.  Lustre 
metallic,  color  iron  black,  streak  black.  In  a  closed  tube 
it  yields  nothing  volatile.  In  an  open  tube  it  gives  anti- 
monial  fumes  and  sulphurous  acid.  It  occurs  also  in 
Gold  Hill  lode,  N.  T. 

a\  The  polybasite  of  the  Comstock  lode  contains  64 
per  cent,  of  silver.  It  gives  in  a  closed  tube,  with  the 
aid  of  the  blow-pipe,  a  reddish  brown  sublimate  with  a 
yellow  .edge.  In  an  open  tube,  white  fumes  arise  and 
some  white  sublimate  deposits.  On  charcoal,  with  the 
reduction  flame,  it  evolves  an  odor  of  garlic.  Played 
upon  with  the  oxydation  flame,  it  gives  out  sulphurous 
acid  and  a  white  coating  of  antimonous  acid.    It  melts 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  41 

to  a  globule  with  a  metallic  lustre.  If  the  hot  blast  is 
changed  suddenly  to  a  cold  one,  and  directed  on  the 
globule,  holding  the  blow-pipe  point  close  to  it,  metallic 
silver  is  emitted.  If  the  cold  blast  is  stopped  too  soon, 
the  silver  will  disappear  again. 

7.  Miargyrite. — Silver  35*8,  antimony  42*8,  sulphur  21, 
H.  =  2  5,  Gr.  =  5-2-5.4.  Lustre  metallic  adamantine, 
color  iron  black,  streak  dark  cherry  red.  In  a  closed 
tube  it  decrepitates,  melts  easily,  and  gives  out  a  subli- 
mate of  sulphide  of  antimony.  In  an  open  tube  sul- 
phurous  acid  and  antimonial  fumes  are  emitted,  deposit- 
ing a  white  sublimate  of  antimonous  acid.  On  charcoal 
it  melts  quietly,  emitting  sulphurous  acid  and  antimo- 
nial fumes.  It  covers  the  coal  with  a  white  coating, 
which  becomes  pink  colored  by  continual  blast.  Melted 
with  soda  a  silver  button  is  obtained,  which,  treated  with 
borax  and  tin,  reacts  on  copper. 

8.  Dark  Red  Silver  Ore  (  Pyrargyrite,  Antimonial 
Blend).  —  Silver  58*9,  antimony  23*4,  sulphur  17*5, 
H.  =  2*5,  Gr.  =  5*7.  Lustre  metallic-like  adamantine, 
color  dark  red,  powder  cochineal-red.  In  a  closed  tube, 
by  the  aid  of  the  blowpipe,  it  yields  a  sublimate  of  sul- 
phide of  antimony,  black  while  hot,  but  varying  from 
red  to  reddish-yellow  when  cold.  In  an  open  tube  it 
gives  antimonial  fumes  and  sulphurous  acid.  On  char- 
coal it  melts  easily  and  deposits  a  white  coating  of  anti- 
monous acid.  With  soda  it  gives  a  silver  globule.  It 
occurs  also  in  the  Gold  Hill  lode,  N.  T. 


42 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


9.  Light  Red  Silver  Ore  (Proustite,  Arsenical  Blend). 
Silver  65*4,  arsenic  15*1,  sulphur  19*4,  H.  =  2*5,  Gr.  = 
5-5-5-6,  color  similar  to  dark  red  silver  ore,  but  lighter. 
Behaves  like  the  preceding,  except  the  arsenical  fumes. 

10.  Xanthocone. — Silver  64,  arsenic  13*4,  sulphur  21*3, 
H.  =  2,  Gr.  =  5-5*2,  color  dull  red  to  clove  brown^ 
powder  yellow.  When  heated  in  a  closed  tube  it  be- 
comes dark  red,  melts  and  gives  some  sublimate  of  sul- 
phide of  arsenic.  While  hot,  it  is  dark  brownish  red, 
and  red  to  reddish-yellow  when  cold.  In  an  open  tube 
and  on  charcoal  it  behaves  like  the  preceding. 

11.  Silver  Fahlerz  (Argentiferous  gray  copper  ore). 
Silver  17-71-31-29,  antimony  26-63-24-63,  sulphur 
23-52-21-17,  copper  25-23-14-81,  iron  3*72-5-98,  zinc 
3*10-0-99,  lustre  metallic,  color  light  steel  gray.  In  a 
closed  tube  it  sometimes  decrepitates,  melts  and  gives, 
by  aid  of  the  blowpipe,  a  dark  red  sublimate  of  tersul- 
phide  of  antimony  with  antimonous  acid.  In  an  open 
tube  it  fuses,  gives  antimonial  fumes  and  sulphurous 
acid.  On  charcoal  it  fuses  easily  and  gives  a  bluish- 
white  coating  of  antimonous  acid  and  antimonial  fumes. 
There  is  also  a  yellowish  coating  close  to  the  test  which 
appears  white  on  cooling.  This  coating  is  created  by 
oxyd  of  zinc. 

a\  The  Reese  River  ore  from  the  Comet  lode  seems  to 
be  a  metamorphosed  silver  fahlerz.  The  sulphur  is  rep- 
resented by  carbonic  acid,  so  that  almost  all  copper  and 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  43 

silver  is  a  carbonate.  It  contains  silver  22*35,  copper  17, 
antimony,  and  some  lead.  It  has  a  dull  greenish-black 
or  black  color,  streak  shining,  powder  greenish-gray.  In 
a  closed  tube  it  yelds  nothing  volatile.  In  an  open  tube 
some  sulphurous  acid  can  be  observed.  On  charcoal 
fuses  slowly,  but  boils  up  suddenly  in  contact  with  glow- 
ing coal,  leaving  a  button  of  silver  and  copper.  This 
button,  when  played  upon  with  the  oxydation  flame  on 
another  spot  of  the  charcoal,  gives  first  a  bluish  coating 
of  antimonous  acid,  then  a  yellow  one  nearer  to  the 
assay  of  the  oxyd  of  lead.  The  silver  can  be  separated 
from  copper  by  cupellation  with  lead. 

b\  The  silver  fahlerz  of  Sheba  lode  (Humboldt)  con- 
tains silver,  8*20,  gold  0*008,  some  antimony  and  lead, 
but  very  little  copper.  It  has  a  light-gray  metallic 
lustre.    It  is  also  called  gray  silver  ore. 

c.  Combination  with  Chlorine,  Bromine,  and  Iodine. 

12.  Horn  Silver  (Chloride  of  Silver).— Silver  75*2, 
chlorine  24*6,  H  =  1*5,  Gr.  =  5*5-5*6,  lustre  adaman- 
tine, color  gray,  greenish  or  blackish,  streak  shining.  It 
looks  like  horn  or  wax.  It  is  translucent  and  may  be 
cut  like  wax.  Occurs  frequently  in  the  Comstock  and 
Gold  Hill  lodes ;  also  in  California.  It  fuses  in  a  candle 
flame.  On  charcoal  it  is  easily  reduced  and  gives  an 
odor  of  chlorine.  If  treated  under  the  reduction  flame 
with  an  addition  of  copper,  it  forms  a  chloride  of  copper 
and  colors  the  flame  azure-blue. 


44 


PROCESSES  of  silver  and  gold  extraction. 


13.  Embolite  (Chlorobromide  of  Silver).— Silver  66*9 
to  75,  H  =  1-1*5,  Gr.  ==  5-3-5*4,  lustre  resinous,  color 
yellowish-green  or  green.  On  charcoal  it  fuses  easily, 
evolves  vapors  of  bromine,  and  gives  metallic  silver. 
Mixed  with  oxyd  of  copper  it  colors  the  flame  greenish- 
blue. 

14.  Bromyrite  (Bromic  Silver). — Silver  57*56,  bromine 
42*44,  H.  =  1-1*5,  Gr.  =  5*8-5*6.  In  a  closed  tube, 
treated  with  bisulphate  of  potassa,  it  emits  brown  va- 
pors. On  charcoal  it  fuses  easily  and  yields  a  globule  of 
silver.  It  is  yellow  or  greenish,  and  may  be  cut  like 
chloride  of  silver. 

15.  lodyrite  (Iodid  of  silver). — Silver  46,  iodine  54, 
H.  ==  1*5,  Gr.  =  5*5.  Lustre  adamantine.  Color  yel- 
low, also  greenish.  It  is  translucent.  In  scale  shape  it 
is  always  lemon-yellow.  When  heated  in  a  closed  tube 
it  becomes  fire  red,  but  assumes  its  former  color  when 
cold.  It  fuses  easily,  and  gives,  by  the  aid  of  the  blow- 
pipe, a  reddish  yellow  sublimate,  getting  lemon-yellow 
on  cooling.  With  bisulphate  of  potassa,  it  emits  beauti- 
ful violet  vapors.  In  an  open  tube  it  gives  an  orange 
sublimate,  lemon-yellow  on  cooling.  On  charcoal  it 
assumes  a  fire  red  color  before  it  fuses,  and  spreads  on 
the  coal  and  yields  many  minute  silver  globules.  With 
an  addition  of  oxyd  of  copper,  it  makes  an  intensely 
green  flame  with  a  bluish  tinge. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  45 

16.  lodid  of  Silver  and  Mercury. — Silver  40-42,  iodine, 
quicksilver,  and  sulphur  (chlorine?)  Color  dull,  dark 
red.  Streak  shining.  Powder  dark  red,  but  changes 
soon  into  lead-gray  if  exposed  to  the  light.  In  a  closed 
tube  it  gives  three  sublimates,  separated  in  rings.  The 
nearest  to  the  assay,  is  black  (sulphide  of  mercury),  the 
second  yellow,  (subchloride  of  mercury?)  the  third  is 
gray  (metallic  mercury).  An  addition  of  bisulphate  of 
potassa  causes  it  to  yield  violet  vapors,  which  come 
from  the  iodine.  In  an  open  tube  it  gives  the  same  sub- 
limate, but  the  black  is  very  slight ;  it  gives  also  yellow 
fumes.  A  gold  particle  in  the  tube  becomes  amalga- 
mated. Litmus  paper  at  the  upper  end  is  colored  red 
by  the  sulphur.  Heated  on  charcoal,  it  turns  black, 
fuses  easily,  and  yields  silver  globules.  Melted  with 
soda,  it  draws  partly  into  the  coal.  If  this  crust  is 
broken  out,  and  laid  on  a  blank  piece  of  silver,  with  a 
drop  of  water,  the  sulphur  in  it  will  cause  a  black  spot 
on  the  silver.  Heated  with  a  small  piece  of  pure  lead, 
it  gives  a  beautiful  green  coating  with  a  yellow  border 
nearest  the  assay.  This  coating  (iodine  and  lead)  is  far 
off  from  the  test.    With  copper  oxyd,  like  the  iodyrite. 

This  mineral  occurs  to  my  knowledge  only  in  the 
Heintzelman  mine  ( Arizona ). 

d.  Combination  with  Antimony. 

17.  Antimonial  Silver. — Silver  77-84,  antimony  23-16, 
H.  =  3*5,  Gr.  =  9-4-9-8.  Lustre,  metallic ;  color  and 
streak,  silver-white.    On  charcoal  it  fuses  easily  to  a 


46 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


globule,  coating  the  coal  white.  A  continual  blast  ren- 
ders the  white  coating  reddish. 

e.  Combination  with  Selenium. 

18.  Nawnannite  (Selenid  of  silver). — Silver  73,  Selen- 
ium 26,  H.  =  2*5,  Gr.  =  8.  Lustre,  metallic  ;  color, 
iron  black.  It  melts  easily  on  charcoal,  but  with  intu- 
mescence in  the  reduction  flame.  It  emits  the  selen- 
ium odor  of  rotten  radish.  With  soda  it  yields  metallic 
silver. 

19.  Eucairite  (Selenid  of  silver  and  copper). — Silver 
43-1,  selenium  31*6,  copper  25*3.  Lustre,  metallic  ;  col- 
or, lead-gray.  On  charcoal  it  melts  to  a  gray  metallic 
globule,  fumes  and  reacts  on  borax  with  copper.  This 
mineral  is  soft,  and  can  be  cut  with  a  knife. 

/.  With  Tellueium. 

20.  Hessite  (Tellurid  of  silver).— Silver  62*42,  tellu- 
rium 36-96,  iron  0*24,  Gr.  =  8-4-8-6.  Lustre,  metallic ; 
color,  lead-gray,  or  steel-gray.  It  is  soft,  and  can  be 
cut  like  lead.  According  to  Mr.  Blake,  this  mineral  is 
found  in  California  also.  He  describes  the  reaction  as 
follows : 

"  In  an  open  tube  the  mineral  fuses  quietly,  coloring 
the  glass  a  bright  yellow  under  assay ;  a  white  or  gray 
sublimate  is  deposited  at  a  short  distance,  immediately 
over  it,  which,  on  being  heated,  fuses  into  transparent 
drops  resembling  oil.    On  charcoal  it  fuses  to  a  leaden 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  47 


colored  globule,  which  on  cooling  becomes  covered  with 
dendrites.  This  globule  flattens  under  the  hammer. 
With  the  addition  of  soda,  a  silver  globule  is  obtained." 

f.  With  Bismutii. 

21.  Bismuth  Silver. — Silver  60,  bismuth  10,  copper  7*8, 
and  some  arsenic.  Lustre,  metallic  ;  color,  tin  white  or 
grayish.  On  charcoal  it  melts  easily,  covering  the  coal 
dark  orange.  It  is  yellow  while  hot,  and  lemon-yellow 
when  cold.  The  oxyd  of  copper  in  it  colors  the  borax 
green  when  melted  on  charcoal. 

g.  With  Mercury. 

22.  Silver  Amalgam. — Silver  34*8-26-2,  quicksilver 
65-2-73.7,  H.  =  3-5,  Gr.  =  13.7-14.  Lustre,  metallic ; 
color,  silver-white ;  brittle.  In  a  closed  tube  the  mer- 
cury sublimates. 

23.  Arquerite — Silver  86*49,  quicksilver  13*51.  It 
behaves  like  the  amalgam. 


CHAPTER  III. 


METALLURGY  OP  GOLD  AND  SILVER  ORES. 

FIRE  ASSAY  OF  ORES. 

The  modes  of  assaying  here  described  are  those  best 
suited  for  the  purpose  of  the  miner  and  millman.  The 
apparatus  and  method  of  procedure  are  as  simple  as  is 
possible,  consistent  with  correctness. 

TOOLS. 

Sec.  17.    A  fine  assay  balance,  as  described  in  Sec.  3. 

A  pair  of  less  delicate  scales,  capable  of  weighing 
about  three  ounces.  The  weights  are  Troy  ounces  ;  one 
ounce  divided  into  Such  a  scale  may  cost  in  San 

Francisco  from  $10  to  $12. 

French  clay  crucibles  No.  7;  some  glass  matrasses; 
dry  cups  (small  crucibles  of  pipe  clay);  a  fine  wire  cloth 
sieve  on  a  wooden  frame,  50  holes  to  the  inch  (2,500  to 
a  square  inch) ;  one  pair  of  crucible  tongs ;  one  pair 
cupel  tongs ;  a  pair  of  pincers ;  a  tooth  brush  and  an 
iron  mortar;  two  or  three  muffles,  10  inches  long,  4 
inches  wide,  and  3  inches  high. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  49 

Cupels. — The  fabrication  of  cupels  requires  a  brass 
mould  and  boneashes.  The  bones  are  burnt  white  for 
this  purpose.  Pieces  not  well  burnt,  showing  a  black 
inside,  do  not  answer.  The  bones  are  then  pulverized 
and  sifted  through  a  fine  sieve,  forty  holes  to  the  inch. 
The  bone  powder  is  sprinkled  with  water,  mixed  and 
rubbed  with  the  hands  till  it  appears  uniformly  moistened 
and  allows  itself  to  be  formed  into  a  ball  by  a  squeeze 
of  the  hand,  without  wetting  it.  The  mould  is  then 
filled  and  beaten  with  the  pestle  by  a  wooden  mallet. 
The  pestle  is  drawn  out  in  a  twisting  way  and  the  cupel 
is  pressed  out  by  the  ball  of  the  hand. 

MATERIALS. 

Sec.  18.  1.  Litharge. — Sifted,  well  mixed,  and  kept 
always  under  cover.  One  ounce  and  a  half,  mixed  with 
10  grains  of  wheat  flower,  melted  in  a  crucible,  will  yield 
a  button,  which  must  be  cupeled,  and  the  weight  of 
the  small  silver  grain  noticed.  This  weight  must  be  sub- 
tracted from  all  assays,  wdiere  this  quantity  of  litharge 
was  used. 

2.  Wheat  Flour. — It  is  used  instead  of  charcoal  to 
reduce  a  part  of  the  litharge  to  lead.  A  mixture  of  one 
hundred  parts  of  soda  and  twelve  parts  of  wheat  flour 
serves  as  a  flux  for  lead  assays. 

3.  Soda  (Carbonate  of  Soda). — If  this  soda  is  crys- 
tallized, it  must  be  exposed  for  some  time  to  the  air,  till 

4 


50  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

it  turns  into  a  white  powder,  thus  losing  half  of  its  water 
of  crystallization.  Bicarbonate  of  soda  or  soda-ash  an- 
swers the  purpose  likewise. 

4.  Glass. — Broken  glass  is  pulverized  in  an  iron  mor- 
tar and  sifted.    It  serves  as  a  flux. 

5.  Salt. — Common  table  salt  is  freed  from  water  of 
crystallization  by  heating  in  a  sheet  iron  box,  like  a 
coffee  roaster,  till  the  decrepitation  ceases.  The  salt 
fuses  quicker  than  the  assay  mixture,  and  prevents  the 
contact  between  air  and  the  assay. 

6.  Iron. — It  is  used  in  small  pieces  of  wire  one-fourth 
or  three-sixteenths  inch  thick,  cut  into  pieces  of  differ- 
ent lengths  from  one-fourth  to  one-half  inch.  The  pur- 
pose is  the  desulphuration  of  the  sulphurets. 

GOLD  AND  SILVER  ASSAY. 

Sec.  19.  The  ore  intended  for  the  assay  must  be 
broken  first  in  small  pieces,  of  which  about  one  pound  is 
taken  without  selection,  afterwards  well  mixed  and 
#  pounded  finer.  From  this  another  portion  is  taken,  about 
three  ounces,  pulverized  and  sifted  through  the  sieve, 
described  in  Sec,  17.  Ores  from  new  lodes  should  be 
assayed  for  the  purpose  of  ascertaining  the  highest 
yield,  and  the  darkest  parts  of  the  ore  selected  and  pul- 
verized. In  taking  samples  of  tailings,  it  is  the  safest 
way  to  procure  three  or  four  boxes  of  about  one  cubic 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


51 


foot  each,  and  have  them  filled  from  the  discharge  at 
different  times,  say  at  the  commencement,  at  the  middle 
and  at  the  end  of  the  discharge  time.  The  box  must  be 
removed  as  soon  as  the  water  reaches  the  brim.  After 
some  hours,  when  the  sand  and  mud  have  settled,  the 
water  is  poured  off,  and  the  contents  of  all  the  boxes 
mixed  and  dried.  These  tailings  are  spread  out,  and 
small  quantities  are  taken  from  different  parts  of  the 
surface  to  the  amount  of  three  or  four  pounds.  This 
sample  is  mixed  well  and  treated  in  the  same  way, 
taking  four  or  five  ounces,  which  must  be  sifted  and 
pounded,  if  any  coarse  sand  is  present.  The  mortar 
must  be  cleaned  carefully  after  pounding  each  sample, 
especially  if  it  was  rich.  In  this  latter  case  the  mortar 
must  be  washed,  or  a  small  piece  of  quartz  pounded  in 
it  and  then  wiped  out  with  a  clean  cloth. 

The  prepared  sample  and  fluxes  are  weighed  in  the 
following  proportion  : 

a.  Ores  or  Tailings  containing  but  little  Sulphurets. 

Ore   250  grains. 

Glass   125  grains. 

Flour   8  grains. 

Litharge   1%  ounces. 

Soda   1  ounce. 

b.  Ores  containing  about  fifty  per  cent,  of  Sulphurets. 

Ore   250  grains. 

Glass   125  grains. 

Iron   50  grains. 

Litharge   \%  ounces. 

Soda  :   1  ounce. 


52  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

c.  Ore  being  nearly  all  Sulphurets. 

The  mixture  is  like  the  preceding,  but  double  the 
amount  of  iron  (one  hundred  grains)  must  be  used. 

The  soda  and  litharge  are  first  introduced  into  the 
crucible,  then  the  balance  of  the  mixture.  By  aid  of 
an  iron  spatula,  the  end  of  which  is  rounded,  ore  and 
fluxes  are  mixed  in  the  crucible  carefully  over  a  sheet 
of  paper.  If  in  mixing,  some  powder  should  be  spilled, 
the  test  can  not  be  considered  proper.  It  is  better  to 
repeat  the  weighing.  If  there  are  several  assays  made 
at  the  same  time,  the  crucibles  must  be  numbered  out- 
side with  red  chalk.  The  charged  crucible  is  tapped 
several  times  against  the  table,  in  order  to  settle  the 
mixture,  and  is  covered  with  salt,  about  one-fourth  of  an 
inch  deep. 

Thus  prepared,  the  assay  is  ready  to  be  melted.  The 
crucible  is  placed  in  the  middle  of  the  furnace,  on  the 
muffle,  or,  if  there  are  two  or  three  assays  to  be  melted, 
the  crucibles,  standing  on  the  muffle  must  touch  each 
other,  leaving  space  between  them  and  the  walls,  as  rep- 
resented in  Fig.  9. 

The  furnace  is  charged  with  charcoal  only  to  the  top 
of  the  crucibles,  and  set  on  fire  by  some  live  coal.  It  is 
not  advisable  to  fill  the  furnace  entirely,  unless  No.  8 
crucibles  are  used,  because  the  assay  effervesces  in  melt- 
ing and  may  overflow.  The  covers  are  taken  off,  the 
charcoal,  by  replacing,  kept  level  with  the  top  of  the 
crucibles  until  the  melting  mass  has  gone  down.  The 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  53 

assays  are  covered  again,  the  furnace  filled  with  coal  to 
the  line,  b,  and  closed  by  an  iron  cover,  a.  The  cupels 
are  placed  now  in  the  muffle,  d,  and  closed  by  the  shut- 
ter, e. 

In  about  half  an  hour  the  charcoal  is  burnt  down  so 
far  that  the  tops  of  the  crucibles  are  exposed.  By  means 
of  the  crucible  tongs  the  covers  are  removed  first,  the 
crucibles  then,  one  after  another,  are  seized  with  a  pair 
of  tongs  (as  represented  in  Fig.  10  cy)  and  the  contents 
poured  into  an  iron  mould  (Fig.  12),  containing  four  or 
five  hollows,  three-fourths  of  an  inch  deep.  In  pouring, 
the  crucible  must  be  kept  close  to  the  mould  and  slowly 
inclined,  by  degrees  almost  perpendicularly,  so  that  the 
slag  may  drop  out  entirely.  This  melting  operation 
takes  nearly  one  hour's  time.  Care  must  be  taken  not 
to  let  the  coal  burn  down  below  the  line,  /,  else  the 
upper  part  of  the  crucible  might  get  too  cool. 

The  lead  button  in  the  mould  is  cooled  off  in  one  or 
two  minutes,  freed  from  slag  by  hammering  it  into  a 
square  shape,  and,  by  means  of  the  cupel  tongs,  intro- 
duced into  the  light  red  hot  cupels.  It  melts  in  a  short 
time,  and  the  oxyd  on  the  surface  draws  to  the  sides  of 
the  cupel.  The  lead  appears  bright,  and  fuming,  and 
minute  spots  of  litharge,  constantly  appearing,  glide  to 
the  sides,  being  absorbed  by  the  cupel  mass.  The  muf- 
fle is  kept  open,  but  the  ash  holes,  g  and  g\  are  closed. 
The  front  edge  of  the  cupels  will  cool  off  by  the  draft, 
and  appear  dark  red  ;  the  button  inside  is  bright.  The 
temperature  must  be  kept  as  low  as  possible,  but  suffl- 


54  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

cient  to  keep  the  button  in  action.  If,  however,  the 
temperature  be  too  low,  and  the  lead,  covered  with  oxyd, 
appearing  dull,  a  piece  of  live  charcoal  is  placed  in  front 
of  the  cupels,  and  the  muffle  is  closed.  By  increasing 
the  heat,  the  button  soon  resumes  its  activity,  the  muffle 
is  opened  again,  and  the  coal  removed.  The  furnace 
must  be  charged  with  charcoal,  so  that  the  muffle  is 
always  covered. 

The  button  becomes  gradually  smaller,  but  looks 
bright  as  long  as  litharge  is  separating  from  it.  As  soon 
as  the  last  particles  disappear,  a  play  of  rainbow  colors 
is  perceived  on  the  remaining  silver  button,  indicating 
the  end  of  the  cupellation. 

Generally,  the  crucibles  are  taken  out  of  the  furnace, 
when  all  the  coal  is  burned  down,  placed  in  a  cool  place, 
and  broken  when  cold.  It  is,  however,  a  great  saving  in 
time,  if  the  melted  mass  is  discharged  in  the  described 
way.  A  comparative  trial  will  show  that  the  results  are 
equal,  if  well  performed. 

If  there  is  not  too  much  importance  connected  with 
the  assay,  the  crucibles  may  be  used  over  four  or  five 
times,  but  care  must  be  taken  not  to  use  crucibles  in 
which  rich  assays  were  made. 

The  silver  button  is  freed  from  adhering  to  boneash 
by  hammering  edgeways  and  weighed.  The  weight, 
multiplied  by  1*16,  gives  the  amount  of  ounces  per  ton 
of  ore  of  2,000  lbs.,  which  may  be  illustrated  by  an 
example.    For  instance,  a  button  is  found  to  weigh — 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  55 

300 
50 
6 

356  X  1*16  —  412*9  ounces  per  ton  of  ore. 

After  weighing,  the  silver  button  is  introduced  into  a 
glass  tube,  adding  about  half  an  ounce  of  pure  nitric 
acid,  and  heated  by  the  alcohol  flame.  It  soon  begins 
to  boil,  emits  reddish-brown  vapors  and  leaves  the  gold, 
if  any  in  the  assay,  in  undissolved  particles  of  a  black 
color  in  the  tube.  The  nitric  acid,  containing  the  dis- 
solved silver  is  poured  off  slowly,  and  the  tube  filled 
with  distilled  water.  When  all  the  particles  of  gold 
have  settled,  this  water  must  be  poured  off  again  care- 
fully and  the  tube  filled  once  more  with  water,  to  the 
brim. 

The  tube  is  then  covered  with  the  dry  cup  and  quick- 
ly turned  over,  as  represented  in  Fig.  11.  The  gold 
falls  to  the  bottom  of  the  cup,  but,  being  very  light  and 
sometimes  in  minute  particles,  the  tube  must  be  kept 
for  a  while  in  this  position,  till  no  suspended  particle  is 
visible.  It  requires  now  some  practice  to  lift  the  tube 
without  spilling  some  water,  which  would  invariably 
carry  out  some  gold.  The  easiest  and  surest  way  is  to 
gradually  lift  up  the  tube,  till  the  water,  the  brim  of  the 
tube  and  the  dry  cup  are  level  (Fig.  11,  a).  A  slide  of 
the  tube  in  the  direction  of  cH  leaves  the  gold  in  the 
cup  undisturbed.  A  slight  tapping  of  the  cup  will 
bring  the  gold  particles  together,  the  water  is  poured 


56 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


off  and  the  cup  dried  over  the  alcohol  flame  till  the 
gold  assumes  a  yellow  color. 

This  gold  is  now  carefully  weighed  and  calculated 
upon  as  follows : 

The  gold  was  found  to  weigh,  for  instance,  Tf  fa,  and 
the  silver  button  before  dissolving  T3o5oV  If  the  gold  is 
subtracted  from  the  silver  which  contained  this  gold, 
we  find  thus  the  pure  silver — 

356-35  =  321  silver  X  1*16  =  372-3  ounces  per  ton. 
and  35  gold  X  H6  =  40-6        "  " 

To  find  the  value,  the  ounces  of  gold  must  be  multi- 
plied with  20*67  and  those  of  silver  with  1-30.  These 
numbers  in  their  fractions  are  not  perfectly  correct,  but 
will  serve  our  purpose.  Continuing  the  calculation  we 
find— 

Silver  =  372-3  ounces  X  1*30  =  $483-99 
Gold  =  40-6      «     X  20-67  =  839-20 

Total  value  $1,323-19  per  ton. 

In  assaying  gold  ore,  the  button  will  not  dissolve  in 
nitric  acid.  In  this  case  it  must  be  melted  (after  weigh- 
ing) on  a  piece  of  charcoal  before  the  blowpipe,  with  the 
addition  of  three  times  its  weight,  of  pure  silver  and 
then  dissolved  and  treated  as  above  described. 

In  case  the  ore  for  the  assay  has  been  weighed  out 
by  half  an  ounce,  equal  to  two  hundred  and  forty  grains, 
the  calculation  is  made  in  the  same  way  as  before  with 
the  exception,  that  the  number  1*215  must  be  substi- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


57 


tuted  for  T16.  The  procedure  of  the  preceding  exam- 
ple would  be  as  follows : 

The  weight  of  the  button  was  three  hundred  and 
twenty-one.  This  multiplied  with  1-215  will  give  the 
amount  of  ounces  per  ton  of  ore  of  2.000  pounds. 

32  (321)  X  1*215  =  390  ounces.  The  quantity  of  fluxes  used  for 
two  hundred  and  fifty  grains  of  ore  will  also  serve  for  half-ounce 
assays. 


LEAD  ASSAY. 


Sec.  20.  In  using  lead  ore  for  the  purpose  of  melting 
silver  ores,  the  amount  of  lead  in  the  ore  must  be  ascer- 
tained. The  lead  ores  of  Nevada  Territory  and  Califor- 
nia are  represented  chiefly  by  sulphuret  of  lead  (galena), 
but  also  to  some  extent  by  carbonate  of  lead. 

The  lead  ore  must  be  sifted  in  the  same  way  as  the 
silver  ore  (Sec.  19)  and  mixed  with  fluxes  in  the  follow- 
ing proportions : 

a.  Ore  containing  Sulphuret  of  Lead. 

Ore   %  ounce. 

Soda  with  12  per  cent,  of  wheat  flour   \%  ounces. 

Glass   %  ounce. 

Iron   100  grains. 

b.  Ore  containing  Carbonate,  Oxyd,  or  Molybdate  of  Lead. 

t  The  mixture  is  the  same  as  that  of  the  ore,  a,  but 
no  iron  is  taken,  as  there  is  no  sulphur  in  the  ore.  If  it 
is  pure  galena,  one  hundred  grains  of  iron  are  used.  If 


58  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

therefore  the  ore,  a,  contains  a  great  deal  of  earthy 
matter  and  less  galena,  or  if  the  ore,  b,  is  mixed  with 
sulphurets,  the  quantity  of  iron  may  be  taken  more  or 
less,  according  to  the  supposed  quantity  of  sulphurets. 
The  melting  is  performed  in  the  same  way  as  is  done 
with  the  silver  assay.  The  lead  button,  resulting  from 
the  assay,  is  weighed  on  the  ounce  scale.  As  one  ounce 
is  divided  the  per  centage  of  lead  in  the  ore  is 
easily  found  by  doubling  the  weight  of  the  button. 


CHAPTER  IV. 


EXTRACTION  OF  GOLD. 

Sec.  21.  The  process  of  extracting  free  gold,  and  the 
manipulation  itself,  is  very  simple,  requiring  only  a 
proper  friction  and  contact  with  quicksilver.  But  there 
are  combinations  of  gold  with  other  substances  in  Cali- 
fornia, refusing  to  liberate  the  gold  by  friction.  Such 
ore,  as  arsenical,  and  some  iron  pyrites,  or  tellurium  of 
gold,  require  a  different  treatment. 

There  are  two  principal  methods  of  gold  extraction.: 
By  amalgamation,  and  by  chlorination. 

A.    BY  AMALGAMATION. 

a.  Amalgamation  in  the  Battery. 

For  this  purpose  the  batteries  are  provided  with  amal- 
gamated copper  plates,  three  to  five  inches  wide,  having 
the  length  of  the  battery ;  one  at  the  discharge,  the 
other  at  the  feed  side ;  the  latter  being  protected  by  the 
iron  feed  plate.  They  are  fixed  with  a  pitch  of  about 
thirty-five  to  forty  degrees  towards  the  dies.    Other  bat- 


60  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

teries  are  so  constructed  as  to  have  sufficient  space  where 
the  amalgam  may  accumulate.  In  this  case,  the  stamps 
are  three  to  four  inches  apart  from  one  another  and  from 
the  sides  of  the  mortar ;  also,  iron  vertical  grates  inside 
the  sieves  are  in  use.  The  amalgam  deposits  readily 
between  the  rods.  The  amalgam  adheres  best  to  copper 
plates  which  are  coated  with  quicksilver.  This  is  per- 
formed by  rubbing  quicksilver  on  the  copper  with  a 
piece  of  cloth  tied  to  a  wooden  handle,  using  some  drops 
of  nitric  acid,  which  may  be  diluted  with  the  fourth  part 
water. 

The  quantity  of  quicksilver  depends  upon  the  quan- 
tity of  gold  in  the  ore.  One  ounce  of  gold  requires  one 
ounce  of  quicksilver,  but  when  the  gold  is  very  fine,  one 
and  one-fourth  to  one  and  one-half  ounces  may  be  used. 
The  quicksilver  is  introduced  every  half-hour,  or  every 
hour  by  the  feeder,  during  the  stamping,  in  each  bat- 
tery, in  portions  of  one-quarter  of  an  ounce,  more  or 
less,  as  the  ore  requires.  This  may  be  observed  at  the 
discharge.  When  the  amalgam  appears  very  hard  or 
dry,  some  more  quicksilver  may  be  used  ;  but  if,  on  the 
contrary,  the  amalgam  is  too  soft,  or  if  quicksilver  drops 
are  perceived,  less  quicksilver  must  be  introduced. 

The  amalgamation  goes  on  very  rapidly.  One  hour 
after  the  quicksilver  is  put  in,  no  yellow  gold  particles 
come  out  of  the  battery,  except  in  cases  when  the  quartz, 
containing  lead,  antimony,  or  other  volatile  metals,  is 
burned  for  the  purpose  of  rendering  it  easier  to  break. 
Many  particles  of  gold  appear  coated,  and  are  discharged 
without  being  amalgamated. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  61 

If  the  proper  proportion  of  quicksilver,  and  the  regu- 
lar times  of  charging  be  observed,  when  the  ore  contains 
heavy  gold  (800  fine),  sixty  to  seventy-five  per  cent,  may 
be  saved  in  the  battery  and  the  copper-plated  platform ; 
but  light  gold  (300  to  400  fine),  like  Washoe  gold,  gives  a 
less  favorable  result.  A  great  many  fine  particles  of  amal- 
gam adhere  together,  involving  also  manganese  scum,  if 
present,  and  form  small  spongy,  blackish  lumps,  which  are 
so  light  as  to  float,  and  on  account  of  being  coated  with 
foreign  matters,  will  not  unite  with  the  accumulated 
amalgam.  Of  this  amalgam  but  very  little  can  be  saved; 
it  floats  over  blankets,  copper  plates,  or  ripples. 

It  is  therefore  an  error  to  use  quicksilver  in  the  bat- 
tery, if  concentration  is  in  use,  and  the  tailings  are  not 
saved.  The  finest  gold  is  easier  retained  by  concentra- 
tion than  this  floating  amalgam.  There  is  also  no  evi- 
dence of  any  advantage  in  battery  amalgamation,  when 
the  whole  mass  of  pulverized  rock  is  amalgamated  in 
pans,  unless  the  mass  or  the  concentrated  part  is 
intended  for  roasting. 

b.   Amalgamation  on  Copper-Plated  Platforms,  Troughs, 

AND  OTHER  COPPER  FIXINGS. 

(Yery  imperfect,  and  mostly  abandoned.) 

c.  Amalgamation  in  Arrastras. 

This  is  a  very  old,  primitive  method,  but  gives  com- 
paratively a  good  result  on  the  free  gold,  if,  under  good 
management,  sufficient  time  is  allowed.    The  construe- 


62  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

tion  is  well  known.  There  is  a  stone  bottom,  ten 
to  fourteen  feet  diameter,  and  wooden  sides,  twenty  to 
twenty-five  inches  high.  Four  or  six  large  stones 
are  dragged  in  a  circular  way  by  chains,  fastened  to 
four  arms  of  the  upright  shaft.  They  make  from  six 
to  ten  revolutions  per  minute,  and  grind  one  and  one- 
half  to  two  tons  of  rock  (broken  in  pieces  as  large  as 
a  hen's  egg  or  smaller)  in  twenty -four  hours.  This  is, 
however,  too  much  for  a  proper  amalgamation. 

When  in  motion,  the  arrastra  is  charged  with  about 
two  hundred  pounds  of  ore,  with  some  water.  One 
quarter  of  an  hour  afterwards  the  balance  of  the  whole 
charge,  from  four  hundred  to  five  hundred  pounds,  is 
introduced.  As  soon  as  the  ore  is  turned  into  mud,  one 
or  two  ounces  of  quicksilver  are  pressed  through  a  dry 
cloth  over  the  thick  pulp.  A  sample  is  taken  from  time 
to  time  with  the  horn  spoon,  washed  and  examined. 
When  free  gold  is  perceived,  after  the  amalgamation  has 
been  going  on  for  some  time,  some  more  quicksilver 
may  be  added.  The  first  charges  require  a  little  more 
quicksilver.  After  four  or  five  hours  the  pulp  is  diluted 
with  water  and  discharged.  The  next  charge  is  treated 
in  the  same  way.  and  so  on  till  one  hundred  or  one  hun- 
dred and  fifty  tons  are  worked  through.  The  quicksilver 
must  be  used  always  in  proportion  with  the  gold,  one  or 
one  and  one-half  ounces  to  an  ounce  of  gold.  The 
amalgam  imbeds  in  the  crevices  of  the  bottom,  and  must 
be  always  dry.  The  use  of  too  much  quicksilver  makes 
the  amalgam  thin,  causes  an  imperfect  amalgamation, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  63 

and  a  loss  in  quicksilver,  which  is  often  found  beneath 
the  bottom  rock. 

d.  Amalgamation  in  Iron  Pans. 

The  pan  amalgamation  is  a  highly  improved  arras tra 
amalgamation,  and  at  present  the  most  perfect  gold 
manipulation.  The  two  conditions,  friction  and  contact 
with  quicksilver,  are  accomplished  in  a  high  degree  by 
Wheelers  pans,  the  description  of  which  will  be  found 
in  Section  50.  The  supposition  that  a  slow  motion  is 
favorable  for  the  amalgamation  is  erroneous  and  en- 
tirely refuted  by  recent  experience.  To  what  degree, 
however,  velocity  may  be  advantageously  increased  is 
not  yet  ascertained  ;  but  sixty  revolutions  per  minute 
of  a  properly-constructed  rnuller  answers  most  satisfac- 
torily, but  the  quicksilver  is  destroyed  by  friction  to 
some  degree. 

There  is  no  chemical  process  required  for  amalgama- 
tion of  gold,  except  with  such  ore  as  is  mentioned  in 
Sec.  21.  By  the  pan  manipulation  the  gold  is  extracted 
as  close  as  ninety -five  per  cent,  of  the  fire  assay.  The 
loss  of  gold  in  the  pans  does  not  result  from  defective 
amalgamation,  .but  from  improper  discharge. 

Ores,  containing  gold  in  such  condition,  that  it  can- 
not be  liberated  by  grinding,  must  be  subjected  to  roast- 
ing without  salt,  before  treating  in  pans. 

The  treatment  of  gold  ores  does  not  differ  from  that 
of  silver  ores,  except  that  no  heat  and  no  chemicals  are 
required. 


64 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


B.    BY  CHLORINATION. 

Sec.  22.  This  process  is  based  on  the  property  of 
chlorine,  which  enables  it  when  placed  in  contact  with 
gold  to  form  a  terchloride  of  gold  without  the  applica- 
tion of  heat.  The  silver,  when  in  the  metallic  state  or 
as  sulphate,  undergoes  the  same  change,  forming  chlo- 
ride of  silver,  but  the  chloride  of  gold  is  soluble  in 
water,  chloride  of  silver  only  in  a  hot  solution  of  salt. 

This  process  is  executed  in  Nevada,  California.  An- 
other establishment,  belonging  to  Mr.  Deetken,  in  San 
Francisco,  beneficiates  concentrated  sulphurets  from 
different  parts  of  California. 

The  chlorination  of  gold  ores  is  a  very  simple  pro- 
cess, still  there  are  some  delicate  points  in  it.  Compara- 
tively, very  few  hands  are  employed ;  and  there  is 
neither  motive  power  nor  steam.  This  process,  if  well 
managed,  extracts  the  gold  very  closely.  Coarse  gold 
particles,  generally  not  found  in  the  tailings,  would 
resist  chlorination,  or  require  too  much  time.  Accord- 
ing to  Mr.  Deetken's  experience,  low  gold  (in  fineness) 
in  the  tailings  is  preferable,  it  being  sooner  transformed 
into  chloride. 

The  tailings  are  subjected  first  to  calcination  in  a 
roasting  furnace,  without  being  sifted.  No  salt  is  used, 
as  it  sometimes  causes  a  loss  of  gold.  The  roasting  is 
performed  in  the  usual  way  by  stirring  the  mass  at  a 
low  temperature  till  all  the  sulphurets  or  arseniurets  are 
decomposed.    An  addition  of  charcoal  powder  favors  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  65 

roasting.  After  six  or  eight  hours,  when  no  odor  of 
sulphurous  acid  is  observed,  the  ore  is  discharged, 
spread  on  a  proper  place  and  cooled.'  The  tailings  or 
ore  is  then  sprinkled  with  water  and  shoveled  over  sev- 
eral times.  A  little  too  dry  or  too  wet  has  a  great  influ- 
ence on  the  result  of  chlorination. 

When  moistened,  the  stuff  is  introduced  into  wooden 
tubs  about  seven  feet  in  diameter  and  twenty-five  or 
thirty  inches  deep.  These  tubs  have  a  prepared  bot- 
tom, which  allows  the  entrance  of  chlorine  gas  from  be- 
neath into  the  mass  of  tailings.  Near  the  bottom  are 
two  holes,  one  for  the  discharge  of  the  solution,  the 
other  communicates  by  a  lead  pipe  with  a  leaden  gas 
generator.  The  generator  is  filled  to  a  certain  height 
with  peroxyd  of  manganese  and  salt.  Sulphuric  acid 
is  introduced  by  a  lead  pipe.  As  soon  as  the  mixture 
becomes  hot,  by  the  fire  underneath  the  generator,  the 
chlorine  gas  commences  to  be  evolved  and  enters  the 
tub  through  the  connecting  lead  pipe. 

After  some  hours  the  whole  mass  is  strongly  pen- 
etrated and  the  greenish  gas  lies  heavy  on  the  tailings. 
The  tub  is  closed  by  a  wooden  cover.  In  this  condition 
it  remains  for  ten  or  fifteen  hours,  when  the  cover  is 
removed  and  clean  water  introduced.  As  soon  as  the 
water  reaches  the  surface  of  the  tailings,  the  discharge 
pipe  is  opened,  and  the  water,  containing  the  dissolved 
chloride  of  gold,  is  led  into  glass  vessels.  An  addition 
of  sulphate  of  iron,  precipitates  the  gold  in  metallic  con- 
dition as  a  black-brown  powder.  If  there  are  silver 
5 


66  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

sulphurets  in  the  ore,  they,  by  roasting  without  salt, 
are  converted  mostly  into  sulphates,  and  in  subsequent 
contact  with  chlorine,  into  chlorides  which  are  not  solu- 
ble in  water,  and  remain  in  the  tailings.  The  gold  is 
therefore  995  fine. 


CHAPTER  V. 


EXTRACTION  OF  SILVER. 

The  extraction  of  silver,  as  practiced  in  Nevada  Ter- 
ritory and  California,  may  be  described  as  follows : 

I.    WET  PROCESS. 

Amalgamation  in  Iron  Pans. 

II.    ROASTING  PROCESS. 

a.  Amalgamation  in  Barrels. 

b.  Amalgamation  in  Veatch  Tubs. 

c.  Amalgamation  in  Iron  Pans. 

nr.   COLD  PROCESS. 

Amalgamation  in  Heaps  (Patio). 

IY.    MELTING  PROCESS. 

Extraction  of  Silver  by  Lead. 


I    WET  PROCESS. 

Sec.  23.  About  two  years  ago,  Mr.  Smith  attracted 
attention  by  his  "  Smith's  Process,"  using  the  ore  without 
roasting,  in  iron  pans  four  feet  in  diameter.    The  sur- 


68  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

face  of  the  bottom  was  diminished  by  a  center-piece  and 
by  many  shoes,  so  that  only  fifty  lbs.  of  ore  could 
be  charged,  and  worked  for  five  to  six  hours.  Since 
that  time  there  has  been  little  improvement  in  the 
exclusively  chemical  part  of  this  process;  but  the  whole 
pan  arrangement  has  been  gradually  so  perfected,  that 
now-a-days  a  four-foot  pan  (Wheeler's)  is  charged  with 
seven  hundred  and  fifty  or  eight  hundred  pounds  of 
ore,  and  the  amalgamation  is  finished  in  three  hours 
including  charge  and  discharge.  But  this  mechanical 
improvement  comprehends  also  that  of  the  chemical 
part.  It  is  known  that  friction  and  iron  decompose 
tough  silver  sulphurets,  without  chemicals.  Friction 
and  iron  are  powerful  chemicals  in  themselves.  Silver 
ore,  treated  with  chemicals  in  a  stone  arrastra  for 
twelve  hours,  will  not  yield  half  so  much  silver  as  one 
Wheeler's  pan  in  three  hours,  without  any  chemicals. 

A  great  advantage  of  this  process,  is  the  working  of 
unroasted  ore.  Dry  crushing,  injurious  to  machinery,  is 
not  required ;  the  immediate  working  of  the  pulverized 
ore  prevents  the  waste,  and  the  silver,  resulting  from 
this  process,  is  generally  very  fine  (970  to  997).  It  is 
comparatively  a  cheap  process.  But,  although  improved, 
the  result  of  this  method  cannot  be  considered  yet  quite 
satisfactory.  In  regard  to  chemicals,  an  important  dis- 
covery can  hardly  be  expected.  Almost  everything, 
between  blue  vitriol  and  tobacco  or  tea  decoction,  which 
reasonably  or  unreasonably  permitted  a  supposition  that 
it  might  effect  the  decomposition  of  the  sulphurets,  has 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  69 

been  experimented  on,  and  yet,  there  are  no  chemicals 
known  by  means  of  which  more  than  fifty  or  sixty  per 
cent,  of  the  silver  can  be  extracted.  If  a  higher  per 
centage  is  obtained,  it  is  on  account  of  the  gold,  or  the 
prevalence  of  silverglance. 

But  the  decomposition  of  silver  sulphurets  does  not 
depend  on  chemicals  alone,  as  is  demonstrated  by 
Wheeler's  pans,  by  which  the  silver  can  be  extracted 
from  ten  to  fifteen  per  cent,  closer  than  in  common  pans. 
The  result,  however,  depends  very  much  on  the  quality 
of  the  ore,  if  the  latter  is  not  roasted.  It  must  be 
observed  that  the  above  per  centage  has  no  reference 
to  gold. 

Not  all  silver  combinations  are  suitable  for  the  wet 
process.  Sufficient  experiments,  however,  have  not  yet 
been  made  as  to  how  the  different  silver  ores  behave  in 
the  pans,  but  it  seems  that  the  difficulty  of  decomposi- 
tion grows  with  the  amount  of  sulphur  in  the  ore,  and 
especially  with  that  of  antimony.  Arsenical  combina- 
tions are  more  easily  worked  than  antimonial.  Pyrites 
of  arsenic,  iron,  and  copper,  are  not  affected  at  all  by 
chemicals.  In  cases  where  such  pyrites  are  argentifer- 
ous, or  antimonial  combinations  are  prevalent,  the  roast- 
ing process  must  be  adopted. 

CHEMICALS  USED  IN  DIFFERENT  MILLS. 

Sec  24.  1.  Sulphate  of  dopper  or  Blue  Vitriol. — It  con- 
sists of  31*72  oxyd  of  copper,  32*14  sulphuric  acid, 


70  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

36*14  water.  It  dissolves  easily  in  water.  In  contact 
with  iron,  metallic  copper  is  precipitated,  and  in  the 
presence  of  quicksilver  amalgamated.  The  sulphuric 
acid  combines  with  iron  oxyd  to  form  sulphate  of  iron. 
If  there  are  no  sulphurets  in  the  ore,  or  if  in  propor- 
tion too  much  blue  vitriol  is  used,  the  amalgam  retains 
almost  all  copper,  which  is  precipitated  with  iron ;  but 
in  contact  wTith  silver  sulphurets,  under  some  circum- 
stances of  galvanic  chemical  action,  the  copper  is  ex- 
pelled again  from  the  amalgam,  and  enters  probably 
into  combination  with  sulphur.  As  soon  as  the  blue 
vitriol  is  introduced,  it  may  be  observed  that  a  great 
part  of  the  bottom  gets  instantly  amalgamated.  The 
surface,  to  which  the  quicksilver  adheres,  is  not  iron, 
but  copper,  being  precipitated  by  iron.  This  copper 
amalgam  is  removed  by  friction  of  the  muller,  and  is 
taken  up  b}^  the  quicksilver ;  and  yet,  the  metal  after 
retorting  and  melting  shows  only  a  trace  of  copper, 
if  the  right  proportion  of  the  blue  vitriol  and  silver 
sulphurets  wras  observed. 

In  nian}^  cases  the  amalgam  after  retorting  looks 
black,  yielding  a  good  deal  of  matt  in  melting.  This 
matt  appears  tough,  is  dark  grayish-blue  in  color,  and 
contains  silver  in  different  proportions  up  to  eighty  per 
cent,  and  sometimes  a  considerable  amount  of  copper. 
The  silver  bar,  however,  is  over  970  fine  (*).    The  matt. 


;:"  The  fineness  must  be  always  understood  in  relation  to  1000  parts  of  the 
metal ;  970  fine  means  970-1000  pure  silver  and  gold,  and  30-100  base  metals. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


71 


when  it  has  a  yellowish  color,  contains  mostly  sulphide 
of  iron. 

The  blue  vitriol  must  be  used  always  in  solution.  In 
this  state  it  is  mixed  sooner  with  the  pulp,  and  kept  in 
suspension,  having  thus  better  opportunity  to  act  imme- 
diately. 

2.  Sulphate  of  Iron,  Copperas,  or  Green  Vitriol. — It  con- 
sists of  27*19  protoxyd  of  iron,  31*02  sulphuric  acid, 
and  41*79  water.  Exposed  to  the  air,  it  turns  into  white 
powder.  This  salt  is  obtained  by  dissolving  iron  in 
diluted  sulphuric  acid. 

3.  Bisulphide  of  Soda. — It  is  composed  of  63  sulphuric 
acid,  37  soda.  This  salt  is  obtained  in  the  acid  factories 
producing  nitric  acid,  from  Chile  saltpetre.  Its  opera- 
tion in  the  pan  is  due  to  the  fact  that  it  readily  parts 
with  one  portion  of  its  sulphuric  acid,  leaving  sulphate 
of  soda. 

4.  Alum. — Potassic  alum  consists  of  33*76  sulphuric 
acid  ;  10*82  alumina  (clay) ;  9*59  potassa ;  45*47  water. 
The  sodic  alum  contains  34*94  of  sulphuric  acid. 

5.  Sulphuric  Acid. — This  chemical  seems  to  act  partly 
by  direct  decomposition  of  silver  sulphurets.  Instantly 
after  being  introduced  into  the  ore,  it  emits  sulphuretted 
hydrogen.  The  silver  may  be  oxydized  by  the  oxygen 
which  is  disengaged  by  the  parting  hydrogen  and  con- 
verted by  the  acid  into  sulphate,  or  it  may  be  set  free  in 


72  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

metallic  condition.  In  both  cases  it  can  be  amalgamated 
without  salt.  But  the  salt,  under  the  action  of  the  sul- 
phuric acid,  creates  muriatic  acid.  This,  however,  may 
be  limited.  A  considerable  part  of  the  sulphuric  acid  is 
engaged  in  dissolving  iron,  forming  sulphate  of  iron, 
setting  hydrogen  gas  free.  There  is  always  so  much 
iron  in  the  pan,  from  the  wear  of  the  stamps  when  the 
ore  is  crushed,  and  from  the  shoes  and  dies  or  bottoms 
of  the  pans,  that  the  pan  itself  is  very  little  eaten  by 
the  acid. 

6.  Common  Salt  (Chloride  of  Sodium). — Salt  cannot 
operate  directly  on  the  sulphurets.  It  does  not  decom- 
pose, but  it  must  be  first  decomposed  by  another  agent, 
before  any  action,  chiefly  chlorination,  can  take  place. 
Sal  ammoniac,  chloride  of  copper,  or  iron,  may  replace 
the  salt  for  the  purpose  of  chloridizing.  But,  as  before 
mentioned,  salt  and  sulphuric  acid  create,  to  some 
degree,  muriatic  acid,  which  acts  also  on  sulphurets. 

7.  Chloride  of  Copjier. — This  salt  is  composed  of  52- 5 
chlorine,  47*4  copper.  It  is  obtained  by  dissolving 
metallic  copper  in  aqua  regia.  To  this  purpose  muriatic 
acid,  with  some  nitric,  is  introduced  into  a  porcelain  or 
enamelled  vessel,  and  some  copper  pieces,  best  in  shape 
of  plates  or  sheets ;  the  acid  will  dissolve  so  much  of 
them  as  to  become  saturated.  Some  heat  hastens  the 
solution,  which  assumes  a  beautiful  emerald-green  color. 
The  chloride  of  copper  seems  to  operate  with  better 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  78 


result  than  blue  vitriol ;  but,  using  this  salt  with  com- 
mon salt,  the  amalgam  obtained  by  this  process  appears 
often  white  and  clean,  crackling  between  the  fingers 
like  pure  silver  amalgam,  still  containing  a  great  deal 
of  sulphurets.  After  retorting,  it  appears  blackish, 
and  renders,  by  melting,  a  pure  silver  bar,  but  also  a 
rich  silver  matt,  sometimes  as  much  as  fifteen  per  cent, 
of  the  bullion,  containing  eighty  per  cent,  of  silver. 
Such  a  result  is  not  always  obtained,  but  under  some 
circumstances,  not  yet  sufficiently  investigated.  When 
experimented  on  in  small  quantities  of  about  twenty- 
five  pounds,  and  the  calculation  made  also  on  the  silver 
in  the  matt,  the  loss  appears  between  fifteen  and  twenty 
per  cent.  In  fact,  however,  the  use  of  sulphate  of  cop- 
per and  salt  amounts  exactly  to  the  same  thing,  because 
the  copper  vitriol,  especially  if  steam  is  introduced,  is 
soon  decomposed  by  the  salt  forming  chloride  of  copper 
and  sulphate  of  soda. 

8.  Siibchloride  of  Copper. — It  consists  of  36  chlorine, 
and  64  copper.  It  is  obtained  by  boiling  metallic  cop- 
per in  copper  chloride,  as  prepared  in  the  above  de- 
scribed way.  It  changes  the  color  from  green  into 
brown,  but  appears  light  green,  when  diluted  with  water, 
giving  a  precipitate. 

9.  Protochloride  of  Iron. — It  consists  of  66  chlorine, 
and  34  iron.  It  can  be  prepared  in  different  ways. 
Small  pieces  of  iron  are  dissolved  in  muriatic  acid  to 


74  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

saturation,  supported  by  a  moderate  heat.  The  iron  is 
then  removed,  or  the  solution  poured  over  in  another 
porcelain  dish*  adding  so  much  muriatic  acid  as  was 
taken  for  the  solution,  and  heated  again,  whereupon 
some  nitric  acid  is  added,  but  carefully,  in  very  small 
quantities,  till  the  boiling  up  ceases.  It  behaves  simi- 
lar to  chloride  of  copper. 

10.  Chloride  of  Iron. — It  is  obtained  by  boiling  or  heat- 
ing metallic  iron  in  aqua  regia  or  muriatic  acid.  It  acts 
favorably  on  the  silver  sulphurets. 

Quantity  of  chemicals 

Per  Ton  of  Ore,  as  used  in  different  Mills. 

Sec.  25.  In  describing  the  quantity  of  chemicals,  as 
used  in  treating  silver  ores,  it  may  be  observed  that, 
according  to  the  amount  of  sulphurets,  also  the  quantity 
of  chemicals  must  be  proportionate. 


a.  Chloride  of  copper  (Sec.  24.  7)   13  pounds. 

Common  salt   60  pounds. 

b.  Chloride  of  iron  (Sec.  24.  10)   13  pounds. 

c.  Sulphate  of  iron   1  pound. 

Sulphate  of  copper   8  pounds. 

Common  salt  -   80  pounds. 


a,  b.  c,  are  calculated  for  ore  containing  from  two  hun- 
dred and  fifty  to  five  hundred  ounces  of  silver  in  sul- 
phurets.   All  chemicals  except  salt  are  used  in  solution. 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  75 


The  salt  is  charged  half  an  hour  before  the  chemicals 
are  put  in. 


d.  Sulphuric  acid   3  pounds. 

Sulphate  of  copper   2  pounds. 

Salt   15  pounds. 

e.  Sulphuric  acid   2  pounds. 

Alum   2  pounds. 

Sulphate  of  copper   1%  pounds. 

/.  Sulphate  of  copper   1-2  pounds. 

Sulphate  of  iron   1-0  pound. 

Sal  ammoniac   0*8  pound. 

Common  salt   2-0  pounds. 

g.  Alum   \%  pounds. 

Sulphate  of  copper   \%  pounds. 

Salt   40  pounds. 

h.  Muriatic  acid   30  ounces. 

Peroxyd  of  manganese   8  ounces. 

Blue  vitriol   10  ounces. 

Green  vitriol   10  ounces. 


i.  Common  salt   15  pounds. 

Nitric  acid   1  to  2  pounds. 

Sulphate  of  iron   1  to  2  pounds, 

k.  Common  salt.   25  pounds. 

Blue  vitriol   2  pounds. 

Catechu   2  pounds. 


These,  and  a  great  number  of  other  recipes,  formerly 
honored  with  the  title  of"  Processes,"  may  not  all  prove 
to  be  the  results  of  experience  or  scientific  specula- 
tion, especially  as  to  the  proportion  and  quantity.  It 
seems  that  there  is  a  boundary  beyond  which  the  ex- 


76  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

traction  of  silver  can  not  be  effected,  whatever  may 
be  done  in  regard  to  quality  or  quantity  of  chemicals, 
or  in  regard  to  time,  if  the  ore  is  not  roasted.  But,  as  a 
matter  of  course,  some  chemicals  work  much  better  than 
others.  Some  ores  are  better  suited  for  the  pan  amal- 
gamation without  roasting  than  others.  The  chemicals 
under  a,  b,  c,  and  d,  will  likely  give  the  most  satisfaction. 

AMALGAMATION  IN  PANS. 

Sec.  26.  The  pans,  especially  the  mullers,  have  different 
shapes ;  but,  although  the  results  of  operations  depend 
considerably  on  the  right  form  of  mullers,  effecting  more 
or  less  perfect  grinding,  it  will  be  sufficient  to  describe 
the  principal  arrangement  of  the  common  pans,  and  of 
the  Wheeler  pans,  the  latter  differing  entirely  from  all 
others  except  Yarney's,  and  lately  Hepburn's. 

(For  a  description  of  the  common  pan,  see  Sec.  49.) 

The  treatment  of  ores  in  iron  pans  is  the  most  simple 
amongst  all  metallurgical  operations.  The  muller  is  pjut 
in  motion,  the  pan  charged  with  some  water,  and  the 
ore,  in  pulverized  condition,  introduced.  A  four-foot 
pan  may  take  one  hundred  and  fifty  pounds  ;  a  five-foot 
two  hundred  and  fifty  or  three  hundred,  and  a  six-foot 
pan  four  hundred  and  fifty  or  five  hundred  pounds  of 
ore.  Wheeler's  pan  of  four-foot,  is  charged  with  seven 
hundred  and  fifty  pounds.  The  quantity  of  water  is 
soon  found  out.  The  ore  must  be  kept  in  a  thickish 
condition.    If  there  is  too  much  water,  there  is  not  only 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  77 

more  friction,  by  the  settling  of  the  sand,  but  also  the 
chemicals  are  more  diluted,  and  the  quicksilver  is  in  one 
mass  on  the  bottom.  But  if,  on  the  other  hand,  the 
pulp  is  too  thick,  the  particles  of  ore  cannot  change 
their  places  quick  enough,  dead  masses  will  occur,  and 
the  amalgamation  is  delayed. 

When  the  pan  is  thus  charged  with  ore,  the  quicksil- 
ver is  next  introduced,  in  quantity  of  thirty-five,  sixty, 
or  eighty  pounds,  according  to  the  sizes  of  the  pans 
above  mentioned.  If  salt  is  used,  it  may  be  added 
immediately  after  the  quicksilver,  and  half  an  hour's 
time  allowed  for  dissolving,  before  other  chemicals  are 
charged.  The  sulphuric  acid  must  be  diluted  with  about 
four  parts  of  water  before  being  introduced.  The  pulp 
of  ore  must  be  kept  as  much  as  possible  in  a  uniform 
condition  in  regard  to  dilution  and  heat,  and  no  boiling 
allowed.  The  right  speed  of  the  muller  is  between  ten 
and  fifteen  revolutions  per  minute.  A  quicker  motion 
is  not  injurious  to  amalgamation,  unless  there  is  too 
much  water  in  the  pan,  or  the  mullers  are  not  set  right, 
and  throw  the  ore  towards  the  sides.  The  temperature 
seems  to  answer  best  when  below  boiling  heat,  but  still 
hot  enough  to  be  inconvenient  to  hold  the  finger  longer 
in  the  pulp  than  just  to  try  its  condition.  Too  much  heat 
is  injurious,  especially  when  sulphate  or  chloride  of  cop- 
per is  used,  causing  a  larger  loss  in  quicksilver,  and  also 
in  amalgam,  which,  assuming  a  black,  rag-like  appear- 
ance, does  not  unite  easily  with  the  other  amalgam,  but 
swims  on  the  quicksilver.    It  parts  in  minute  particles, 


78  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

and  is  liable  to  escape  in  discharging  the  tailings.  Such 
black  amalgam  rubbed  in  a  porcelain  mortar,  gives  a 
great  deal  of  black  powder,  consisting  of  some  silver  sul- 
phurets  and  sulphide  of  copper,  resulting  from  sulphate 
of  copper,  probably  by  action  on  sulphurets  of  silver. 

Treating  the  ore  cold,  using  sulphuric  acid  and  salt, 
the  result,  in  regard  to  the  quantity  of  amalgam,  does 
not  differ  much ;  but  after  retorting  and  melting,  the 
warm  amalgamation  gains  from  five  to  seven  per  cent,  on 
the  value  of  the  bar.  Chloride  of  copper  and  chloride 
of  iron  allow  cold  amalgamation,  but  warm  amalgama- 
tion may  be  better  for  some  qualities  of  ore. 

After  a  run  of  three  or  four  hours,  during  which  time 
the  ore  is  ground  very  fine,  water  is  introduced,  and  the 
pulp  diluted,  so  that  all  quicksilver  and  amalgam  can 
join  in  one  mass  on  the  bottom,  which  may  require  half 
an  hour's  time.  There  are  generally  three  discharge 
holes  to  each  pan.  The  lowest  one  serves  for  discharg- 
ing quicksilver  and  is  level  with  the  bottom  or  even 
below  it,  communicating  with  a  groove,  which  runs  to 
the  centerpiece.  The  uppermost  hole  is  opened  and 
the  tailings  discharged,  under  a  constant  stream  of 
water,  into  the  pan.  After  one-quarter  of  an  hour  the 
lower  plug  is  removed,  continuing  the  discharge  for 
another  quarter  of  an  hour.  Both  holes  are  plugged  up 
again,  the  pan  charged  with  ore  and  treated  as  before. 
The  quicksilver  may  be  taken  out  once  or  twice  a  week 
or  oftener  according  to  the  richness  of  the  ore. 

In  discharging  the  tailings,  some  amalgam  is  always 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  79 

carried  out,  especially  at  the  end  of  the  operation,  when 
the  coarser  sand  is  washed  off.  To  prevent  the  loss  of  this 
amalgam,  agitators  are  applied.  They  consist  of  tubs, 
two  or  three  feet  in  diameter,  and  ten  or  twelve  inches 
high,  with  a  vertical  shaft,  on  which  four  arms  are  fixed, 
having  vertical  stirrers  as  represented  in  Fig.  ^7.  But 
it  is  evident  that  one  agitator  for  many  pans,  as  is  the 
general  usage,  is  not  sufficient ;  it  is  only  a  repetition 
of  the  first  washing.  The  greatest  part  of  the  amalgam 
goes  out  again.  These  agitators  differ  very  much  in 
construction  and  size,  none,  however,  offer  a  satisfactory 
result.  The  most  proper  and  time-saving  way,  in  dis- 
charging the  pans  where  a  constant  stream  of  clear 
water  can  be  obtained,  is  the  use  of  one  or  two  general 
agitators,  six  or  eight  feet  in  diameter,  in  which  the 
tailings  are  discharged,  leaving  the  quicksilver  with  a 
part  of  the  ore  always  in  the  pan.  The  tailings  are  not 
diluted,  unless  the  stuff  is  too  thick.  In  this  case  some 
water  may  be  introduced  into  the  pan  before  discharg- 
ing, but  not  so  much  as  to  allow  a  separation  of  slime 
and  fine  sand.  From  the  agitator  the  tailings  run  off  in 
a  small  stream  (three-eighths  of  an  inch  thick)  into  a  five- 
foot  pan  in  which  a  continual  stream  (an  inch  in  diameter) 
of  clear  water  flows,  as  described  in  Sec.  27.  This  strong 
dilution  under  a  constant  stream  permits  a  very  close 
separation  of  amalgam  which  unites  with  the  quicksilver 
in  the  pan.  Such  pans  are  of  better  service,  when 
the  continual  discharge  is  arranged  in  the  centre  like 
Knox's  pans,  because  the  motion  of  the  muller  (fifteen 


80  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

to  eighteen  revolutions  per  minute)  creates  a  strong 
current  on  the  periphery. 

When  the  tailings  are  discharged,  there  is  always  a 
good  deal  of  sand  left  in  the  pan,  partly  to  save  time, 
but  chiefly  on  account  of  quicksilver  and  amalgam,  of 
which  a^  the  end  of  the  operation,  more  is  carried  out  in 
proportion. 

Whenever  the  quicksilver  gets  thick  by  the  amalgam 
or  at  the  close  of  the  week,  the  lowest  hole  is  opened, 
after  the  tailings  have  been  removed  by  the  usual  dis- 
charge. The  quicksilver  runs  into  buckets,  but  some 
of  it  remains  in  the  pan  and  must  be  taken  out  with  the 
scoop.  By  means  of  a  piece  of  blanket  and  clear  water, 
the  quicksilver  is  washed  perfectly  clean,  and  poured 
into  a  filter,  of  sugar-loaf  shape  (see  Fig.  18),  of  strong 
canvas  or  duck.  The  quicksilver  runs  through  the 
cloth,  leaving  the  amalgam  in  the  filter,  which  generally 
must  be  pressed  over  again  through  a  cloth  by  hand  or 
a  press.  This  amalgam  must  be  separated,  the  metal 
from  the  quicksilver,  by  retorting  (see  Sec.  42). 

All  the  sand,  sulphurets,  and  amalgam  particles  from 
the  last  discharge  and  cleaning  of  the  quicksilver,  must 
come  back  into  the  pan  with  the  next  charge.  If,  how- 
ever, the  sulphurets  and  metallic  iron  from  the  wear  of 
the  shoes  accumulate  too  much,  forming  a  heavy  stuff, 
which  generally  retains  a  great  deal  of  amalgam,  it  is 
better  to  treat  it  separately  in  a  pan  with  addition  of 
one,  or  one  and  a  half  per  "cent,  of  sulphuric  acid,  and 
to  save  all  these  tailings,  which  contain  such  silver  com- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


81 


binations,  as  resist  decomposition  in  pans.  These  tail- 
ings, if  accumulated  to  several  tons,  must  be  roasted 
with  four  or  five  per  cent,  of  salt,  and  treated  in  pans 
without  chemicals. 

AMALGAMATION  IN  WHEELER'S  PANS. 

Sec.  27.  The  amalgamation  in  Wheeler's  pans  (see 
Sec.  50,  Figs.  24,  25)  does  not  differ  much  from  that  of 
others,  but  the  peculiarity  of  discharging  tailings  and 
quicksilver  every  time,  at  once,  which  is  based  on  the 
construction  and  motion  of  the  muller,  requires  attention 
to  some  points,  which  partly  influence  the  good  results 
of  the  amalgamation.  A  quick  and  fine  grinding  at  the 
speed  of  fifty  to  sixty  revolutions  depends  also  on  the 
quality  of  the  shoes  and  dies.  Soft  shoes  will  stand 
according  to  the  quality  of  ore  thirty  to  forty  days, 
while  hard  ones  of  white  iron,  will  last  ten  to  fifteen 
days  longer,  doing  at  the  same  time  better  grinding. 
The  only  inconvenience  of  the  hard  shoes  and  dies  con- 
sists in  the  brittleness  of  the  iron.  On  this  account  they 
must  be  removed  in  time,  so  that  not  more  than  three- 
fourths  of  an  inch  are  worn  off,  leaving  one-fourth  of  an 
inch  in  thickness.  If  this  be  neglected,  and  the  shoes 
become  thinner,  a  trifling  foreign  hard  matter  may  effect 
the  break  of  shoes  or  dies,  and  cause  a  break  in  the  yoke 
or  something  else. 

The  advantage  of  a  quick  and  prompt  grinding  will 
be  found  indirectly  in  saving  silver  ore,  because  it  allows 
6 


82  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  use  of  coarser  ore  in  the  pan.  It  is  a  known  fact 
that  the  finer  the  ore  is  crushed,  especially  wet,  the 
more  silver  ore  will  be  turned  into  slime,  of  which  a 
great  deal  will  be  carried  out  by  the  water  (*).  Crush- 
ing dry,  the  loss  in  dust  will  increase  with  the  fineness 
of  the  sieves. 

It  is  therefore  advisable  to  crush  coarse  and  to  grind 
fine.  Using  common  pans,  it  is  preferable  to  pulverize 
the  ore  as  fine  as  possible  in  order  to  save  time  and  the 
shoes  of  the  pan,  especially  the  bottom.  Wheeler's  pan 
performs  the  pulverization  much  quicker  and  cheaper 
*than  the  battery  does,  at  a  certain  size  of  grain. 

The  guide-blades  must  be  kept  always  close  to  the 
muller,  in  order  to  prevent  ore  and  quicksilver  from  fol- 
lowing the  motion  of  the  muller,  thus  forcing  the  mass  to 
the  centre  and  under  the  muller.  The  present  construc- 
tion is  such,  that  the  muller  cannot  follow  the  wear  of 
the  shoes  for  more  than  about  half  an  inch.  The  grind- 
ing becomes  imperfect.  In  this  case,  which  may  happen 
once  in  a  week,  the  key  and  screw  which  fasten  the 
yoke  to  the  driving  shaft,  must  be  loosened,  and  the 
shaft  raised  half  an  inch,  paying  attention  that  the  mul- 
ler, after  all  is  fixed,  can  be  raised  above  the  dies  at  least 
one-eighth  of  an  inch.    When  this  is  done,  the  guide- 


*  That  the  slime  is  very  difficult  to  work  in  pans  to  advantage  is  known  to 
every  millman.  On  this  account  and  because  the  slime  is  often  richer  than  the 
coarser  sediment,  especially  if  brittle|silver  sulphurets  are  present,  the  coarse 
crushing  is  preferable.  It  was  even  observed  that  more  quicksilver  scum  is 
formed  in  treating  slime  than  in  working  coarser  material. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  83 

blades  have  to  be  lowered  by  the  screw  on  top  of  the 
shaft,  so  as  to  have  it  again  close  to  the  muller.  If  hard 
shoes  are  used,  this  adjusting  may  not  be  required  for  a 
longer  time.    It  takes,  however,  only  a  few  minutes. 

The  consistence  of  the  pulp  must  be  thickish,  but  still 
so,  that  a  lively  motion  on  the  sides  and  between  the 
guide-blades  is  perceptible.  If  the  motion  be  too  slack, 
some  water  must  be  added.  In  regard  to  amalgamation, 
a  little  more  or  less  water  is  not  so  important  as  it  is  for 
the  separation  of  amalgam  in  the  agitators. 

Steam  must  be  introduced  three  or  four  inches  above 
the  muller,  for  if  too  close  to  the  bottom,  the  pipes  re- 
quire frequent  cleaning.  The  temperature  can  be  kept 
near  to  the  boiling  point.  There  is  no  necessity  of  a 
steam  chamber.  The  direct  use  of  steam  in  the  pulp 
does  not  interfere  with  the  required  consistency,  but 
allows  a  considerable  saving  of  .fuel.  Eight  Wheeler's 
pans,  if  the  boiler  is  proportionate,  require  half  a  cord 
of  wood  in  twenty-four  hours. 

In  regard  to  chemicals,  after  several  months'  run  at 
Col.  Raymond's  mill  on  Carson  River,  experience  proved 
that  the  use  of  chemicals  is  entirely  useless  in  treating 
Ophir  ore.  I  made  comparative  runs  for  many  weeks, 
and  found  that  experience  confirmed  that  a  better  result 
was  obtained  without  any  chemicals  whatever.  The  use 
of  them  was  therefore  abandoned  at  the  Dayton  mills. 
It  is,  however,  a  fact,  that  in  treating  silver  ore  in  com- 
mon pans,  the  use  of  chemicals  always  gives  a  better 
result.    It  can  not  be  supposed,  therefore,  that  the 


84  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

chemicals  prevent  a  perfect  amalgamation  in  Wheeler's 
pans,  but  the  amalgam  is  in  a  different  condition,  more 
liable  to  be  ground  into  a  black  floating  powder.  This 
is  also  the  reason  that  it  seems  as  if  the  quicksilver 
were  protected  by  the  chemicals  against  being  ground 
to  scum,  because  the  black  powdered  quicksilver  is  less 
visible. 

The  loss  of  quicksilver  could  not  have  been  ascer- 
tained yet,  as  it  is  not  advisable  to  take  out  the  dies 
on  account  of  cleaning.  As  a  matter  of  course,  the 
quicksilver  must  be  turned  into  scum  to  some  degree, 
but  considering  the  better  yield  and  expelling  of  chemi- 
cals, these  pans  can  afford  to  lose  some  quicksilver.  In 
the  course  of  manipulation,  however,  a  great  deal  of  this 
scum  is  regained. 

It  is  unquestionable  that  the  iron  under  favorable 
circumstances  decomposes  the  silver  sulphurets  just  as 
well  or  better  than  the  best  chemicals ;  but  if,  on  ac- 
count of  improper  arrangement  of  grinding,  the  action 
of  iron  on  sulphurets  is  effected  in  a  limited  degree, 
the  chemicals  will  then  assist.  It  happens  often  that  in 
cleaning  the  agitator,  when  no  chemicals  are  applied  in 
the  pans,  a  strong  smell  of  sulphuretted  hydrogen  is  ob- 
served, which  arises  from  the  decomposition  of  sulphur- 
ets. In  washing  the  tailings,  after  the  iron  has  been 
extracted  with  the  magnet,  blue  sulphurets  can  hardly 
be  discovered.  The  difficulty  in  stating  the  loss  of  sil- 
ver lies  partly  in  the  inconvenience  of  taking  out  the 
dies,  in  order  to  effect  a  perfect  cleaning,  as  it  is  almost 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  85 

impossible  to  place  the  dies  back  again  as  level  as  be- 
fore, but  the  difficulty  is  chiefly  found  in  the  attempt  to 
get  a  reliable  average  sample  for  the  assay,  especially  if 
wet  crushing  is  going  on.  The  sulphurets  and  gold  are 
always  concentrated  in  the  vats,  where  the  ore  falls  in 
from  the  battery,  and  every  inch  in  it  shows  a  different 
amount  of  silver.  The  next  vat  shows  the  same  differ- 
ence, having,  besides,  already  so  much  slime  that  a  mix- 
ing for  the  purpose  of  having  the  metal  equally  distrib- 
uted in  the  mass,  is  impossible  without  drying. 

The  calculations  on  the  superiority  of  Wheeler's  pans, 
at  least  to  the  present  date,  are  derived  from  the  com- 
parative yield  and  the  appearance  of  the  tailings,  ac- 
cording to  which  these  pans  seem  to  yield  at  least  ten 
per  cent,  more  than  the  best  common  pans.  To  find  the 
real  loss  of  silver  and  quicksilver,  it  would  require  dry 
ore,  each  charge  well  mixed,  sampled,  and  weighed,  and 
one  pan  and  agitator  exclusively  for  this  purpose.  This 
could  not  have  been  performed  yet. 

A  great  difference  as  to  the  result  will  be  found  in  a 
comparative  working  of  the  finest  sediment  (the  slime) 
which  glides  between  the  mullers  of  the  common  pans 
almost  motionless,  as  if  it  were  one  mass,  while  in 
Wheeler's  pans  the  slime  is  forced  under  the  muller 
with  the  same  speed  as  the  ore. 

When  the  muller  is  in  motion,  so  much  water  is  intro- 
duced that  it  plays  over  the  rim  of  the  muller ;  then 
seven  hundred  and  fifty  pounds  of  wet  ore,  or  six 
hundred  of  dry,  are  charged,  and  if  it  is  perceived 


86  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

that  the  motion  of  the  ore  is  not  lively  enough,  more 
water  is  added.  The  pulp  should  not  cover  the  guide- 
blades.  After  this,  one  hundred  pounds  of  quick- 
silver are  poured  into  each  pan.  The  amalgamation 
and  grinding  continue  for  three  hours.  A  longer  amal- 
gamation does  not  appear  to  give  a  better  result.  The 
plug  of  the  hole  which  is  nearest  to  the  bottom  is 
taken  out,  and  the  whole  mass  discharged.  The  pan  is 
charged  immediately  as  before.  The  charge  and  dis- 
charge can  be  effected  in  five  minutes.  Of  the  hundred 
pounds  of  quicksilver,  which  were  introduced,  only  fifty 
or  sixty  pounds  were  discharged  with  the  ore ;  the  bal- 
ance remains  between  the  dies.  All  the  subsequent 
charges  take  fifty  pounds.  Several  hundred  pounds  of 
quicksilver  must  be  kept  at  hand,  to  replace  such  as  re- 
mains with  the  amalgam  in  the  agitator. 

Wheeler's  agitator  (see  Sec.  51),  being  eight  feet  in 
diameter,  has  such  a  swift  motion  on  the  periphery,  that, 
treating  the  tailings  in  the  usual  way,  by  diluting  with 
clear  water,  a  great  deal  of  amalgam  is  carried  out. 
The  discharge  from  the  upper  hole,  where  the  mud  and 
very  fine  sand  with  much  water  flows  out,  is  free  of 
amalgam,  but  after  all  the  mud  has  been  removed  and  the 
lower  hole  opened,  the  floating  amalgam,  which  cannot 
reach  the  bottom  on  account  of  the  sand  (which  settled 
in  consequence  of  the  dilution),  escapes  with  the  tail- 
ings. The  loss  increases  with  the  speed  and  also  with 
the  coarseness  of  the  tailings.  If  the  speed  is  reduced, 
the  motion  near  the  centre  will  be  too  slow. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  87 

After  different  experiments  I  adopted  the  following 
method,  by  which  the  above  difficulties  are  avoided: 
Three  inches  above  the  bottom  (see  Fig.  23)  there  is  a 
three-eighth-inch  pipe,  through  which  the  tailings  flow 
out  in  a  thin  stream  continually,  so  that  in  the  course  of 
three  hours,  if  three  pans  are  discharged  into  one  agi- 
tator, the  tailings  are  down  to  the  level  of  the  pipe. 
The  quicksilver  and  amalgam  have  time  enough  to 
sink  by  degrees  to  the  bottom,  and  those  particles 
which  escape  through  the  three-eighth-inch  pipe  are 
also  saved. 

No  water  is  needed  in  the  agitator,  but  the  pulp  must 
have  the  proper  consistency  when  discharged.  The 
amalgam  accumulates  round  the  centre-bowl.  It  will  be 
found  that  this  amalgam,  and  that  from  the  bowl,  is 
richer  in  gold  than  that  further  ofi^  while  the  fine  amal- 
gam carried  out  through  the  pipe  contains  only  one-half 
of  the  amount  of  gold  which  is  found  in  the  average  of 
the  agitator  amalgam.  It  occurs  often  that  a  great  part 
of  the  amalgam  deposits  in  the  amalgamating  pans, 
sometimes  accumulating  on  the  sides,  and  accidentally 
on  the  muller,  which,  if  perceived  at  the  discharge,  must 
be  taken  out,  else  it  might  accumulate  to  fifty  pounds, 
or  more,  pressing  the  muller  on  one  side,  and  thus 
causing  a  very  unequal  wear  of  the  shoes.  At  other 
times,  no  deposit  of  amalgam  takes  place  in  the  pans,  or 
one  pan  may  retain  as  much  as  one  hundred  pounds, 
when  another  has  none  at  all.  It  seems  that  this  appear- 
ance depends  on  a  variable  electric  condition  of  the 
iron. 


88  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

When  the  pans  are  discharged,  the  quicksilver  runs 
on  the  inclined  bottom  to  the  centre,  joining  the  quick- 
silver in  the  bowl,  coming  out  by  the  siphon,  whence  it 
is  taken  and  returned  to  the  pans,  fifty  pounds  to  each 
charge.  The  amalgam  accumulates  also  in  the  bowl, 
preventing  finally  the  passage  through  the  siphon.  In 
this  case  the  agitator  must  be  cleaned.  To  this  purpose, 
when  the  last  discharge  is  effected,  the  lowest  one-half 
inch  pipe  is  opened,  and  the  tailings,  when  level  with 
the  half-inch  pipe,  are  discharged  by  the  hole  on  the 
inclined  bottom  near  the  bowl.  The  tailings  from  this 
last  discharge  are  led  into  a  separate  box,  whence  it  can 
be  transferred  immediately  into  the  other  agitator,  or  if 
only  one,  back  into  Wheeler's  pan.  The  agitator  is  then 
stopped,  the  black  stuff  from  the  bottom,  which  is  very 
rich  in  fine  amalgam,  removed,  the  quicksilver  strained, 
and  the  bowl  filled  again  with  quicksilver  after  the 
siphon  was  also  cleaned.  All  this  can  be  done  in  three 
hours,  so  that  the  agitator  is  ready  for  the  subsequent 
discharge  of  the  pans.  The  shoes  of  the  agitator  must 
be  run  suspended  about  one-eighth  of  an  inch  above  the 
bottom,  in  order  to  allow  the  settling  of  sulphurets  and 
amalgam. 

If  the  ore  contains  a  great  deal  of  sulphurets  of  such 
a  nature  that  a  part  of  them  do  not  yield  up  their  silver 
without  roasting,  the  agitator  may  be  used  as  a  concen- 
trator at  the  same  time,  by  screwing  up  the  shaft,  on  the 
arms  of  which  the  shoes  are  fastened,  for  one-eighth  of 
an  inch  or  more  every  day. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  80 

All  the  black  stuff  from  the  agitator  must  be  worked 
over  in  a  common  five  or  six-foot  pan  without  the  addi- 
tion of  quicksilver,  and  the  tailings  saved  to  be  roasted. 

Each  agitator  must  have  one  four  or  five-foot  pan  for 
the  reception  of  the  tailings,  coming  out  of  the  one- 
eighth  inch  pipe.  The  discharge-hole  of  this  pan,  about 
three  inches  above  the  bottom,  is  always  open,  so  that 
the  tailings  have  only  a  passage  through  the  pan,  the 
muller  of  which  may  make  twelve  or  fifteen  revolutions. 
The  fine  amalgam,  and  especially  the  quicksilver  scum, 
would  escape  from  this  pan  to  the  greatest  part,  if  not 
diluted.  A  continual  stream  of  clear  water,  therefore, 
through  a  pipe  an  inch  or  three-quarters  of  an  inch  in 
diameter,  is  indispensable.  Twenty  or  thirty  pounds  of 
quicksilver  are  introduced  into  the  pan  in  order  to  col- 
lect the  amalgam. 

In  some  mills  Wheeler's  pans  are  discharged,  using 
only  the  upper  hole,  retaining  thus  the  most  of  the 
quicksilver.  This  mode  saves  the  trouble  of  handling 
the  fifty  pounds  required  for  each  charge  ;  but  the  amal- 
gam, accumulating  in  the  quicksilver,  is  too  much  ex- 
posed to  grinding,  causing  thus  a  richer  quicksilver 
scum,  of  which  a  considerable  part  is  lost. 

Wheeler's  pans  have  been  improved  lately  by  Mr. 
Hepburn.  The  improvement  seems  to  be  important. 
Without  having  a  larger  diameter,  the  conical  bottom 
offers  a  larger  grinding  surface.  The  whole  arrange- 
ment is  simplified.  On  account  of  the  inclined  bottom, 
no  guide-blades  are  required.    One  of  these  pans  is 


90  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

charged  with  1,000  pounds,  so  that  four  tons  of  ore  may 
be  worked  in  twenty-four  hours  by  one  pan,  requiring 
about  two  and  one-half  horse-power  each.  In  regard  to 
the  amalgamation,  there  will  be  probably  the  same 
result  as  obtained  by  Wheeler's.  All  that  was  said  in 
relation  to  the  manipulation  with  Wheeler's  pans  can  be 
applied  also  to  Hepburn's. 


n.   EOASTING  PROCESS. 

Sec.  28.  The  roasting  of  silver  ore,  for  the  purpose  of 
converting  all  the  silver  into  a  chloride,  no  matter  in 
what  condition  it  may  occur,  either  in  the  metallic  state, 
or  in  a  sulphuret,  arsenide  or  antimonial  silver,  in  order 
to  make  it  fit  for  easy  decomposition  and  subsequent 
immediate  amalgamation,  has  been  adopted  in  several 
extensive  works  of  Nevada  Territory.  There  may  be 
some  kinds  of  silver  ore,  which  under  certain  circum- 
stances can  be  treated  raw  in  pans  very  advantageously, 
even  if  there  be  a  greater  loss  of  silver.  Nevertheless, 
the  high  importance  of  roasting  can  not  be  overlooked, 
this  being  in  many  instances  the  surest  and  the  only 
way  to  beneficiate  such  silver  combinations  as  refuse  to 
deliver  the  silver  by  amalgamation  without  roasting. 
There  is  no  silver  ore  which  can  not  be  treated  success- 
fully by  means  of  roasting.  The  patio  or  pan  amalgama- 
tion, working  so-called  "  rebellious  "  ores,  must  resort  to 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  91 

roasting,  or  else  exclude  such  ores  from  the  manipula- 
tion. 

In  regard  to  the  importance  of  roasting,  which  in 
course  of  time  may  be  more  appreciated,  a  thorough 
description  of  this  process  appears  necessary.  More- 
over, it  is  entirely  impossible  to  carry  on  a  rational  and 
correct  roasting  according  to  the  quality  of  ore,  or  in 
regard  to  a  special  object,  if  the  chemical  actions  during 
the  roasting  are  not  regarded  or  understood.  It  is  in- 
dispensable to  get  acquainted  with  the  theory  of  this 
process,  of  which  the  most  important  actions  will  be 
considered. 

Three  agents  are  active  in  roasting :  the  oxygen  of 
the  air,  the  hydrogen  of  the  water-vapors  of  the  air  and 
fuel,  and  the  chlorine  of  the  salt.  (By  the  term  "roast- 
ing" I  here  always  mean  " chlorination  roasting")  But 
as  the  decomposition  of  salt  by  heat  alone  is  very  im- 
perfect, sulphur  is  another  important  agent,  the  pres- 
ence of  which  is  by  all  means  required.  The  decompo- 
sition of  salt  is  effected  by  sulphuric  acid  in  the  form  of 
vapor,  and  by  sulphates,  produced  by  the  oxygen  of  the 
air  and  the  sulphur  of  the  sulphurets  in  the  ore.  If, 
therefore,  the  silver  were  combined  with  antimony  or 
arsenic,  with  but  little  or  no  sulphurets,  the  chlorination 
would  be  very  imperfect.  In  this  case  an  addition  of 
two  or  three  per  cent,  of  calcined  green  vitriol  (sulphate 
of  iron)  is  required. 

The  principal  object  in  roasting  must  be  first,  the 
production  of  sulphates.    The  iron  pyrites  and  other 


92  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

sulphurets,  when  red  hot  and  acted  upon  by  the  oxygen 
of  the  air,  change  into  sulphates  by  oxydation  of  the 
sulphur  to  sulphuric  acid.  The  sulphuric  acid  can  not' 
unite  with  the  metal  of  the  sulphuret  under  decompo- 
sition, unless  it  becomes  an  oxyd.  One  part  of  the  sul- 
phuric acid,  therefore,  transfers  oxygen  to  the  metal, 
being  thus  reduced  to  sulphurous  acid,  while  the  metal 
becomes  an  oxyd  and  combines  with  another  part  of 
sulphuric  acid  to  a  sulphate. 

During  this  process,  which  is  performed  at  a  low  heat, . 
the  salt  is  almost  entirely  indifferent,  so  that  it  is  imma- 
terial whether  it  is  charged  at  the  same  time  with  the 
ore,  or  two  hours  later. 

As  soon  as  the  sulphates  are  formed,  and  no  odor  of 
sulphurous  acid  observed,  the  heat  must  be  increased. 
The  decomposition  of  salt  begins,  being  performed  in 
two  different  ways : 

1.  The  sulphate  of  iron  principally,  and  other  sul- 
phates, emit  sulphuric  acid  in  vapor,  which,  in  contact 
with  saltj  forms  sulphate  of  soda,  setting  free  the  chlo- 
rine in  a  gaseous  form.  One  part  of  the  oxygen  of  the 
sulphuric  acid  is  transferred  to  the  sodium  of  the  salt, 
oxydizing  it  to  soda,  which,  uniting  with  another  part 
of  sulphuric  acid,  forms  sulphate  of  soda,  while  the  chlo- 
rine absconds,  combining  with  free  metals  in  chlorides 
when  in  contact  with  them,  and  decomposes  sulphurets 
in  such  a  way,  that  one  part  of  the  chlorine  combines 
with  the  sulphur  in  volatile  chloride  of  sulphur,  while 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  93 

another  part  unites  with  the  freed  metal  of  the  sulphuret 
in  a  chloride. 

2.  The  other  way  of  decomposition  of  salt  differs  in 
its  result,  not  emitting  chlorine  gas,  but  forming  chlo- 
rides during  the  act  of  decomposition.  The  sulphate  in 
contact  with  salt  enters  into  an  exchange  of  compounds. 
The  sulphuric  acid  combines  with  the  soda  of  the  salt 
to  sulphate  of  soda,  and  the  chlorine  with  the  metal  of 
the  sulphate  to  a  chloride,  the  oxygen  of  the  metaloxyd 
oxyclizing  the  sodium.  The  chlorination  of  metals  ac- 
cordingly is  performed  by  the  direct  action  of  chlorine 
gas  on  the  metals  and  sulphurets,  and  by  contact  of  salt 
with  sulphates. 

During  this  process,  besides  the  chlorine  gas,  hydro- 
chloric acid  in  vapor  is  created.  The  rrvdroehloric  or 
muriatic  acid  arises  partly  by  the  action  of  water-ab- 
sorbing sulphuric  acid  on  the  salt,  whereby  the  sodium 
is  oxydized  by  the  oxygen  of  the  water,  while  its  hy- 
drogen unites  with  the  chlorine  to  form  hydrochloric 
acid  in  the  form  of  gas.  The  muriatic  acid  is  also  formed 
by  the  contact  of  chlorine  gas  with  compounds  of  hy- 
drogen, for  instance  carburetted  hydrogen.  The  chlo- 
rine, by  its  affinity  for  hydrogen,  decomposes  the  com- 
pounds of  the  latter  elements.  It  is  also  produced  by 
the  contact  of  steam  with  volatile  chlorides,  as  chlorides 
of  antimony,  zinc,  lead  or  copper,  etc.,  reducing  the 
metals  to  oxyds,  or  the  silver  to  a  metallic  state,  which, 
however,  in  contact  with  hydrochloric  acid  or  chlorine, 
is  turned  again  into  a  chloride. 


94  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

The  circumstances,  accordingly,  under  which  the  for- 
mation of  hydrochloric  or  muriatic  acid  takes  place,  are 
various,  but  always  when  water-vapors  enter  the  porous 
mass  of  ore. 

Behavior  of  Chlorine  Gas. 

Sec.  29.  It  has  been  mentioned  already  that  chlorine 
gas  acts  directly  on  sulphurets.  Under  the  action  of 
chlorine  gas  the  following  changes  occur : 

a.  The  Iron  (with  sulphur  or  arsenic)  changes  into 
protochloride  of  iron  (Fe  CI),  but,  exposed  to  the  air, 
into  sesquichloride  (Fe2  CI3).  This  chloride  becomes 
volatile  and  is  sublimable.  If  in  this  condition  it  meets 
gaseous  products  of  burning  fuel  containing  vapors  of 
water,  or  hot  air  containing  steam,  a  mutual  decompo- 
sition takes  place,  resulting  in  oxyd  of  iron  and  gaseous 
hydrochloric  acid. 

b.  Manganese  (combined  with  sulphur)  changes  into 
protochloride  of  manganese  (Mn  CI).  It  is  not  volatile. 
Water-vapors  decompose  it  into  sesquioxyd  and  gaseous 
muriatic  acid. 

c.  Zinc  (combined  with  sulphur)  changes  into  proto- 
chloride of  zinc  (Zn  CI).  It  melts  before  it  is  red  hot, 
and  becomes  volatile  when  red  hot.  In  contact  with 
steam,  it  forms  oxyd  of  zinc  and  hydrochloric  acid. 

d.  Lead  (in  combination  with  sulphur)  changes  very 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


95 


slowly  into  chloride  of  lead  (Pb  CI).  It  melts  easily. 
In  contact  with  red  hot  air  it  evaporates  partly,  while 
another  part,  evolving  chlorine,  changes  into  a  com- 
pound of  oxyd  of  lead  and  chlorid  of  lead,  which  is  not 
volatile. 

e.  Copper  (combined  with  sulphur)  changes  partly 
into  sesquichloride  of  copper  (Cu2  CI),  partly  into  proto- 
chloride  (Cu  CI),  according  to  the  action  of  more  or  less 
chlorine  at  a  higher  or  lower  temperature.  Both  com- 
binations are  inclined  to  evaporate.  When  red  hot,  the 
chloride  changes  into  sesquichloride,  emitting  half  of  its 
chlorine,  by  which  sulphurets  are  decomposed.  Under 
the  action  of  steam  a  mutual  decomposition  takes  place, 
creating  gaseous  hydrochloric  acid  and  oxyd,  or  sequi- 
oxyd  of  copper,  the  latter  being  converted  into  oxyd  by 
contact  with  the  air. 

/.  Silver  (native  and  in  combination  with  sulphur) 
changes  slowly  into  chloride  of  silver  (Ag  CI.)  It  be- 
comes volatile  only  at  a  high  temperature. 

g.  Gold  (free  or  combined  with  arsenic,  antimony,  or 
tellurium)  changes  when  in  a  very  fine  pulverized  state, 
at  a  low  heat,  into  terchloride  of  gold  (Au  CI3).  It 
emits  two  parts  of  chlorine,  below  red  heat,  forming 
chloride  of  gold  (Au  CI).  Red  heat  changes  it  into 
metallic  gold. 

h.  Arsenic  (with  other  metals  and  sulphur)  is  trans- 


96  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

formed  into  a  very  volatile  terchloride  of  arsenic  (As 
CI3). 

L  Antimony  (with  other  metals  or  sulphur)  changes 
into  terchloride  of  antimony  (Sb  CI3).  It  is  like  the 
terchloride  of  arsenic,  very  volatile. 

Behavior  of  Hydrochloric  Acid. 

Sec.  30.  The  gaseous  hydrochloric  acid  in  contact 
with  metallic  silver  unites  with  it  at  a  high  temperature 
to  form  chloride  of  silver.  The  hydrogen  is  set  free. 
It  behaves  in  like  manner  with  the  sulphurets  and 
arsenides,  of  which  the  most  are  decomposed  in  such  a 
way  that  chlorides  of  metals  are  formed,  while  the  sul- 
phur or  arsenic  combines  with  the  hydrogen. 

Behavior  of  Salt. 

Sec.  31.  When  the  roasting  of  ore  has  advanced  so 
far  that  considerable  quantities  of  chlorides,  which  are 
partly  volatile,  are  formed,  under  the  action  of  chlorine, 
and  hydrochloric  acid  in  contact  with  salt  and  sulphates, 
some  of  the  salt,  not  previously  decomposed,  evaporates. 
These  salt  vapors,  and  those  of  the  volatile  chlorides 
transfer  chlorine  to  undecomposed  sulphurets  or  arsen- 
ides, or  to  already  present  sulphates,  arsenates,  or  anti- 
monates,  or  to  free  oxyds.  Chlorides,  which  are  disposed 
to  transfer  chlorine  to  such  metals  in  combination  with 
sulphur  or  arsenic  as  possess  more  affinity  to  chlorine, 
than  themselves,  are,  besides  salt,  protochloride  of  iron, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  97 

protochloricle  of  copper,  also  the  chlorides  of  zinc,  lead, 
and  cobalt. 

a.  Metallic  Silver  in  contact  with  salt  changes  partly 
into  chloride  of  silver,  probably  in  such  a  way  that  the 
silver  decomposes  the  salt  in  the  same  proportion  as  the 
sodium  takes  up  carbonic  acid  from  the  gaseous  pro- 
ducts of  burning  fuel. 

b.  Sulphurets  in  contact  with  salt  are  not  decomposed 
directly.  The  sulphurous  acid,  however,  in  contact  with 
the  air,  creates  sulphuric  acid,  which  acts  on  the  sodium, 
freeing  thus  the  chlorine,  by  which  the  formation  of 
chlorides  in  the  not  yet  decomposed  sulphurets  are 
effected. 

c.  Arsenides  are  not  changed  by  the  salt.  They 
oxydize,  evolve  arsenous  acid,  and  are  converted  into 
arsenates.  Only  a  very  slight  decomposition  of  salt 
takes  place.  The  presence  of  sulphates,  however,  vola- 
tile chlorine,  or  gaseous  hydrochloric  acid,  effects  the 
chlorination. 

d.  Oxyds  of  Metals,  with  the  exception  of  the  oxyd  of 
silver,  are  changed  very  little  or  not  at  all  by  salt.  The 
oxyd  of  silver  readily  giving  up  its  oxygen,  changes 
perfectly  into  chloride  of  silver,  if  sufficient  salt  be 
present.  A  small  portion  of  the  oxyds  of  copper  and 
lead  are  changed  into  chlorides. 

7 


98  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

e.  Sulphates. — Sulphates  decompose  the  salt  by  mutual 
exchange  of  compounds.  The  sulphate  of  lead  changes 
into  chloride  of  lead,  which,  evaporating  in  contact  with 
air,  emits  one  part  of  its  chlorine,  being  reduced  to  a 
combination  of  chloride  and  oxyd  of  lead.  The  sul- 
phate of  copper  changes  into  chloride  of  copper.  This 
becoming  volatile,  evolves  chlorine  gas,  and  forms  sesqui- 
chloride  of  copper,  which  is  less  volatile. 

Sec.  32.  The  ores  intended  for  roasting  must  be 
examined  not  only  in  regard  to  the  quality  and  quan- 
tity of  sulphurets,  but  also  in  regard  to  the  earthy  mat- 
ters accompanying  the  ore.  It  is  not  immaterial  whether 
the  ore  contains  carbonate  of  lime  or  quartz.  If  there 
is  a  great  deal  of  lime  in  the  ore,  it  absorbs  sulphuric 
acid,  forming  sulphate  of  lime,  remaining  in  this  con- 
dition through  the  whole  process,  without  being  decom- 
posed. On  this  account  calcareous  ore  requires  so  much 
more  sulphurets  or  sulphate  of  iron  as  is  necessary  to 
change  all  the  lime  into  sulphate.  Talcose  ores  behave 
like  the  calcareous.  Silicia  or  quartz,  if  abundant,  in 
presence  of  steam  decomposes  some  of  the  salt,  when 
red  hot,  forming  silicate  of  soda  and  hydrochloric  acid, 
the  importance  of  which  has  been  mentioned  (see  Sec. 
30).  This  behavior  of  these  earths  shows  that  it  is 
disadvantageous  to  submit  pure  calcareous  or  talcose 
ores  to  roasting,  and  that  in  such  a  case  quartzose  ore 
must  be  added,  if  possible. 

The  qtiantity  of  sulphurets  in  the  ore  is  important,  a 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  99 

certain  amount  of  it  being  required  to  decompose  so 
much  salt  as  is  necessary  for  chlorination.  In  Freiberg 
(Germany),  it  was  the  rule  to  subject  only  that  ore  to 
roasting  which  contained  enough  sulphurets  to  give 
twenty-five  or  thirty  per  cent,  of  matt  (sulphide  of  iron), 
when  assayed  for  that  purpose.  If  less  matt  was  ob- 
tained, the  ore  had  to  be  mixed  with  other  ore,  or  so 
much  iron  pyrites  was  added  that  the  required  quantity 
of  sulphurets  was  obtained.  The  second  class  ore  of  the 
Ophir  and  Mexican  claims  in  the  Comstock  lode,  con- 
sisting of  pure  decomposed  quartz,  contains  silver  sul- 
phurets, with  a  small  proportion  of  iron  pyrites,  yielding 
from  six  to  eight  per  cent,  of  matt.  The  roasting  with 
salt,  however,  gives  a  satisfactory  result,  which  must  be 
attributed  chiefly  to  the  pure  quartzose  condition  of  the 
ore. 

If  the  ore  contains  an  abundance  of  sulphurets,  the 
roasting  must  be  performed  without  salt,  for  about  two 
hours,  till  the  greatest  part  of  the  sulphur  is  driven  off, 
otherwise  it  would  bake,  and  cause  an  imperfect  roast- 
ing. 

The  quantity  of  sulphurets  has  a  great  influence  on 
the  result  of  roasting.  Ore  like  that  of  the  Ophir  or 
Mexican  mines,  containing  silverglance,  polybasite,  brit- 
tle silver  ore,  native  silver  and  gold,  some  iron,  and  but 
little  copper  pyrites,  will  give  a  good  result  by  roasting, 
even  when  less  attention  is  paid  to  the  time  and  dili- 
gent stirring,  than  for  instance  with  the  so-called  "  base 
metal  ore,"  which  abounds  in  copper  pyrites,  zinc-blend, 


100  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

sulphuret  of  lead,  etc.  The  presence  of  base  metals 
causes  a  higher  loss  in  silver.  The  chloride  of  silver  is 
not  volatile,  except  at  a  high  temperature  (Sec.  29,/). 
But  it  has  been  observed  that,  in  the  presence  of  base 
metal  chlorides,  the  chloride  of  silver  volatilizes  also. 
The  increased  heat  increases  the  volatilization,  but  de- 
composes the  base  metal  chlorides.  By  keeping  a  low 
heat,  the  loss  of  silver  is  less  if  the  zinc-blend  is  not 
argentiferous,  the  latter  requiring  a  higher  heat  to  effect 
decomposition.  But  in  roasting  at  a  low  heat,  the  base 
metal  chlorides  remain  in  the  ore,  and  cause  more  loss 
of  quicksilver  in  the  subsequent  amalgamation,  and 
require  more  metallic  iron  in  the  barrels ;  besides,  the 
bullion  contains  a  great  deal  of  base  metals.  In  treat- 
ing such  ore  in  the  roasting  furnace,  the  application  of 
steam  is  advantageous,  creating  hydrochloric  acid  by 
the  decomposition  of  chlorides,  at  the  same  time  becom- 
ing a  decomposing  agent  for  the  sulphurets.  The 
hydrogen  of  the  steam  decomposes  also  the  chloride  of 
silver,  which,  upon  being  reduced  to  a  metallic  condition, 
by  its  affinity  for  chlorine,  in  turn  decomposes  the  hydro- 
chloric acid.  The  silver  may  thus  change  repeatedly 
from  metallic  condition  to  the  chloride,  while  the  base 
metal  chlorides  are  reduced  to  oxyds,  and  in  that  state 
do  not  interfere  with  the  amalgamation. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


101 


A.    ROASTING  OF  SILVER  ORES 
For  the  Barrel  and  Veatch's  Steam  Amalgamator. 

Sec.  33.  The  silver  ore  for  the  modes  of  amalgama- 
tion without  friction,  as  shown  by  long  experience,  must 
be  free  from  metallic  gold,  or  it  must  be  extracted 
before  the  ore  is  subjected  to  roasting,  as  is  done  in  the 
"  Silver  State  Eeduction  Works,"  on  Carson  River. 
After  roasting,  the  gold  is  not  like  silver,  in  a  soluble 
and  easily  decomposable  condition,  but  in  a  metallic 
state,  generally  coated  with  some  oxyd,  especially  if  sul- 
phuret  of  lead  occurs  in  the  ore.  This  renders  the 
amalgamation  of  gold  much  more  difficult.  Also,  metal- 
lic silver,  when  roasting  is  performed  without  salt,  using 
charcoal  and  saw-dust  for  the  purpose  of  converting  the 
silver-combinations  of  the  ore  into  the  metallic  state,  will 
be  imperfectly  amalgamated  in  the  barrels. 

The  ore  does  not  require  to  be  very  fine  for  the  pur- 
pose of  roasting,  but  it  must  be  fine  on  account  of  amal- 
gamation. Vertical  wirecloth  sieves  at  the  battery, 
with  nine  hundred  holes  to  the  square  inch,  if  dry  crush- 
ing is  in  use,  or  sixteen  hundred  holes  when  wet  crush- 
ing is  preferred,  on  account  of  extracting  gold,  will 
answer  the  purpose. 

The  pulverized  dry  ore  is  spread  on  a  platform  and 
mixed  with  from  six  to  twelve  per  cent,  of  salt,  accord- 
ing to  the  richness  and  quality  of  the  ore.  It  seems, 
however,  that  six  per  cent.,  as  used  in  one  of  the 


102  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Washoe  valley  works  for  ore,  assaying  from  seventy-five 
to  one  hundred  dollars  per  ton,  may  not  be  sufficient, 
still  the  result  is  considered  quite  satisfactory.  Very 
rich  ore  may  require  fifteen  or  twenty  per  cent,  of  salt. 
In  dry  crushing,  the  salt  may  be  mixed  with  the  ore  in 
the  right  proportion  before  going  to  the  battery.  This 
mode  of  mixing  is  the  most  perfect  and  most  con- 
venient. 

The  Bed  Hot  Furnace  (see  Sec.  53,  Figs.  29,  30)  is 
charged  with  eight  hundred  or  one  thousand  pounds  of 
ore,  and,  by  means  of  iron  hoes  spread  over  the  bottom 
of  the  furnace.  If  the  ore  is  moist,  or  rich  in  sulphurets, 
the  heat  is  kept  low.  The  workman  commences  to  stir 
the  ore  with  the  hoe  or  an  iron  rake,  back  and  forward 
across  the  hearth,  moving  slowly  from  the  bridge 
towards  the  flue  and  back.  When  the  ore  is  perfectly 
dry,  appearing  very  movable,  almost  flowing,  the  heat 
must  be  increased.  Continual  stirring  is  required,  in 
order  to  expose  new  ore  on  the  surface,  thus  facilitating 
the  oxydation.  If  there  is  a  great  amount  of  sulphurets 
in  the  ore,  the  sulphur  commences  to  burn  when  the 
ore  gets  dark  red  hot,  evolving  so  much  heat  that  the 
firing  must  be  suspended  for  about  one  hour  and  a  half, 
but  the  stirring  continues,  touching  all  spots  and  corners 
of  the  hearth.  After  a  great  part  of  the  sulphur  is 
burnt  off,  the  temperature  will  sink,  and  the  ore  appear 
dark.  The  temperature  must  be  raised  again  by  firing. 
The  formation  of  sulphates  is  going  on,  disengaging  a 
large  quantity  of  sulphurous  gas.   The  ore  at  the  bridge 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  103 

will  be  heated  much  more  than  on  the  opposite  side. 
The  roaster  must  take  the  trouble  of  changing  the  ore 
from  the  bridge  to  the  flue,  and  the  cooler  ore  to  the 
bridge,  several  times.  If  lumps  are  perceived  in  the 
ore,  they  must  be  beaten  to  powder  by  an  iron  hammer- 
like instrument  with  a  long  handle.  After  three  or  four 
hours  roasting,  according  to  the  amount  of  sulphurets, 
no  sulphurous  acid  is  perceptible.  The  temperature 
must  be  increased  to  a  light  red  heat.  The  formation 
of  sulphates,  arsenates,  antimonates,  and  oxyds  is  almost 
completed.  The  chlorination  has  commenced,  and  as 
the  increased  heat  is  rapidly  going  on,  white  fumes 
arise,  and  the  gases  and  vapors  evolved  have  a  sharp, 
acrid  odor,  consisting  of  some  sulphurous  acid,  chlorine 
gas,  hydrochloric  gas,  chloride  of  sulphur,  chlorides  of 
iron  and  copper,  etc. 

The  ore  assumes  a  spongy  or  woolly  condition,  increas- 
ing in  volume.  In  the  presence  of  sufficient  copper  the 
flame  is  colored  blue  by  the  chloride  of  copper.  After 
one  hour's  roasting,  at  an  increased  heat  and  with 
diligent  stirring,  the  chlorination  is  finished.  The  ore  is 
discharged  by  the  back  door  or  the  discharge  hole  in 
the  bottom,  although  the  fumes  and  gases  are  still 
being  evolved. 

If  there  is  a  great  deal  of  copper  and  other  base 
metals  in  the  ore,  the  roasting  may  require  more  time 
in  order  to  decompose  the  chloride  of  copper  and  sul- 
phates, the  presence  of  which  in  the  amalgamating 
barrels  or  tubs  destroys  not  only  more  iron,  but  increases 


104  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  heat  too  much,  causing  an  injurious  division  of  the 
quicksilver  into  small  particles  and  scum.  The  base 
metal  chlorides,  reduced  by  the  iron,  enter  into  the 
amalgam  and  make  it  impure.  The  time  for  decompo- 
sition must  be  prolonged  in  the  barrels  before  the  quick- 
silver is  introduced,  otherwise  a  destruction  of  mercury 
would  follow. 

The  decomposition  of  the  base  metal  chlorides  can  be 
effected  in  the  furnace  either  by  carbonate  of  lime  or  by 
heat,  the  latter  requiring  more  time.  The  carbonate  of 
lime  in  pulverized  condition  decomposes  the  chlorides 
and  sulphates,  but  not  the  chloride  of  silver.  The  addi- 
tion of  lime  rock,  after  the  heat  has  been  increased, 
must  be  made  gradually  in  regard  to  the  quantity,  com- 
mencing with  two  per  cent.,  till  the  required  amount  for 
a  certain  class  of  ore  is  found.  It  may  require  as  much 
as  six  per  cent.  The  first  portion  of  lime  is  introduced 
by  a  scoop,  spreading  it  over  the  ore  and  well  mixed. 

A  small  portion  of  the  ore  is  then  taken  in  a  porce- 
lain cup  or  glass,  and  mixed  with  some  water  by  means 
of  a  piece  of  iron  with  a  clean  metallic  surface.  If  the 
iron  is  coated  red  with  copper,  or  if  the  water  is  bluish, 
some  more  lime  is  required.  After  the  lime  is  charged, 
half  an  hour  must  be  allowed  for  reaction.  When 
another  test  does  not  show  the  above  signs  of  soluble 
copper,  or  only  in  a  slight  degree,  the  charge  can  be 
taken  out.  In  the  absence  of  lime,  wood  ashes  may  be 
used.  If  too  much  lime  or  ashes  is  used,  the  amalgama- 
tion is  injured,  and  a  greater  loss  of  silver  will  be  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  105 

result.  The  chloride  of  copper  will  also  be  decomposed 
by  longer  roasting  and  increased  heat,  and  samples 
should  be  taken  in  the  same  way  as  before  to  ascertain 
the  decomposition  of  those  chlorides. 

One  furnace  requires  two  men  by  day  and  two  men 
by  night  in  order  to  keep  up  continual  stirring,  firing, 
charging,  and  so  forth.  The  Central  mill  at  Virginia 
City  employs  two  men  at  a  time,  attending  three  fur- 
naces. The  stirring  is  performed  at  intervals ;  roasting 
six  or  seven  hours,  in  treating  rich  ore.  Other  works 
having  poorer  ore  finish  the  roasting  in  four  and  a  half 
and  five  hours. 

The  ore  after  having  been  roasted  contains  from  five 
to  fifteen  per  cent,  of  lumps,  which  are  not  roasted 
thoroughly,  and  contain  some  undecomposed  sulphurets, 
sulphates,  and  chlorides.  These  lumps  are  separated 
from  the  fine,  well-roasted  ore,  pulverized,  and  with  the 
addition  of  two  or  three  per  cent,  of  salt  are  roasted 
again  for  two  hours.  The  ore  is  sifted  through  two 
sieves.  One  has  64,  the  other  2,500  to  3,600  holes  to 
the  square  inch.  The  lumps  which  do  not  pass  the 
coarse  sieve  are  pulverized  under  stamps  and  reroasted. 
The  ore  which  passes  the  first  sieve  and  stops  at  the 
second  is  ground  fine  and  delivered  with  the  fine  sifted 
ore  for  amalgamation. 

In  the  Central  Mill  there  is  no  grinding  after  roast- 
ing. The  ore  is  pulverized  under  a  set  of  small  stamps 
and  sifted  while  the  coarser  particles  are  constantly 
elevated  to  the  battery. 


106  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

B.    ROASTING  OF  SILVER  ORES 
For  Pan  Amalgamation. 

Sec.  34.  The  roasting  of  ore  for  the  purpose  of  amal- 
gamating in  iron  pans,  differs  from  the  already  described 
procedure,  in  so  far  as  a  perfect  chlorination  of  all  the 
silver  in  the  ore  is  not  absolutely  required.  Consoli- 
dated fragments  or  lumps  formed  during  the  roasting 
are  not  injurious.  The  extraction  of  gold  before  roast- 
ing is  not  necessary. 

The  sulphates,  remaining  in  the  lumps,  and  such  as 
were  not  changed  into  chlorides  by  improper  roasting, 
are  partly  decomposed  in  the  pan  by  the  iron,  but  most 
of  them  are  converted  into  chlorides  by  the  salt,  which 
always  remains  in  small  quantities  in  the  ore  after  roast- 
ing. This  salt  dissolves  in  the  pan  and  changes  the  sul- 
phates, which  are  also  soluble,  into  chlorides,  they  being 
decomposed  by  the  iron  and  amalgamated.  The  quick- 
silver, when  present  in  the  pan,  takes  also  part  in  the 
decomposition,  being  thus  converted  into  subchloride  of 
mercury  or  calomel,  which,  unlike  chloride  of  mercury, 
not  being  decomposed  by  the  iron,  causes  a  loss  in  quick- 
silver. 

The  sulphate  of  silver,  soluble  in  hot  water,  will  be 
decomposed  by  iron  into  metallic  condition,  combining 
with  the  quicksilver  to  an  amalgam.  It  would  appear, 
therefore,  that  roasting  without  salt,  for  the  purpose  of 
producing  sulphate  of  silver,  which  is  easily  beneflciated 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  107 

in  the  pans,  would  be  more  economical  by  saving  salt.  * 
It  is,  however,  very  difficult  to  transform  all  the  silver 
into  a  sulphate.  The  sulphates  of  iron  and  copper  must 
be  formed  before  the  sulphuret  of  silver  can  be  changed 
into  a  sulphate,  and  if  there  is  not  sufficient  sulphuric  acid 
emitted  by  other  sulphates,  a  great  deal  of  the  sulphu- 
ret will  be  decomposed  into  sulphurous  acid  and  metallic 
silver,  the  presence  of  which  must  be  avoided.  If  arse- 
nic and  antimony  be  present,  arsenate  and  antimonate 
of  silver,  which  will  escape  the  amalgamation,  will  be 
formed.  A  great  part  of  the  arsenate  and  antimonate 
of  silver  will  be  changed  into  sulphate  of  silver,  but  not 
all,  especially  if  the  ore  is  poor  in  iron  sulphurets.  On 
the  other  hand,  if  the  heat  is  kept  too  high,  the  sulphate 
of  silver  will  be  reduced  to  a  metallic  state,  which,  as 
before  remarked,  must  be  avoided ;  because,  while  the 
sulphate  is  not  volatile,  the  metallic  silver,  by  means  of 
oxydation,  evaporates,  and  deposits  itself  in  cooler  places 
in  a  metallic  condition,  emitting  oxygen,  causing  thus  a 
loss. 

The  chlorodizing  roasting  requires  less  attention,  and 
gives  a  better  result.  The  sulphurets,  which  may  re- 
main in  the  ore  undecomposed  after  roasting,  will  be 
reduced  in  the  pan  by  predominant  chlorides  and  sul- 
phates. Sulphates  alone  effect  very  imperfect  decom- 
position of  sulphurets  in  the  pan. 

Mr.  Sutro's  furnace  for  this  purpose  (at  Dayton,  N.  T.) 
is  twelve  feet  by  thirteen,  offering  about  one  hundred 
and  fifty  square  feet  of  hearth  surface.    The  furnace  is 


lOS*         PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

*  charged  with  2,000  pounds  of  ore  with  two  per  cent,  of 
salt,  or  when  pan-tailings  are  subjected  to  roasting,  the 
ore  of  which  had  been  treated  with  chemicals  and  salt, 
the  latter  is  not  added  at  all.  Two  men  are  employed 
at  a  time  at  each  furnace  for  twelve  hours.  The  stirring 
is  kept  up  constantly  at  a  low,  dark  red  heat  four  hours 
long,  when  the  ore  is  considered  well  roasted  and  with- 
drawn. It  contains  a  great  many  lumps,  so  that  sifting 
and  pulverizing  are  required,  chiefly  on  account  of  the 
imperfect  pan  arrangement.  In  using  Wheeler's  or 
Hepburn's  pans,  it  is  not  necessary  to  pulverize  the 
roasted  stuff!  The  lumps  are  not  formed  in  the  furnace, 
but  are  the  consequence  of  the  fine  muddy  condition  of 
pan-tailings.  In  roasting  dry  ore,  or  well  dried  and  pul- 
verized pan-tailings,  the  lumps  are  formed  in  small  pro- 
portion. This  roasted  ore  is  then  introduced  into  the  pan 
like  unroasted  ore,  and  amalgamated  in  the  usual  way. 
A  great  deal  of  the  base  metals  will  enter  the  amalgam, 
if  such  occur  in  the  ore,  but  a  strange  appearance  is  the 
iron  amalgam  which  is  always  obtained  in  a  certain 
quantity  in  treating  pan-tailings.  It  separates  in  melt- 
ing, swimming  on  the  fused  metal  in  lumps,  when  it 
must  be  removed  and  melted  over  with  more  fluxes. 
But  it  sometimes  happens  that  all  the  amalgam  after 
retorting  appears  black,  spongy,  and  very  light,  contain- 
ing from  forty  to  fifty  per  cent,  of  iron.  In  this  case  the 
result  in  regard  to  silver  extraction  is  unfavorable.  This 
black  retorted  iron  amalgam,  only  the  result  of  certain 
old  pan-tailings,  must  be  worked  over,  treating  it  like 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  109 

ore,  in  a  pan  with  quicksilver  and  some  sulphuric  acid. 
The  iron  entering  the  amalgam  is  derived  principally 
from  the  wear  of  dies  and  shoes,  being  in  metallic  con- 
dition, but  after  six  hours'  roasting,  most  of  it  is  finally 
converted  into  an  oxyd.  Some  chloride  of  iron  or  other 
combinations  may  still  remain  in  a  very  limited  propor- 
tion. It  is  therefore  difficult  to  account  for  the  reason 
why,  and  under  what  conditions  the  iron  is  amalgamated, 
as  experiments  on  ores  containing  metallic  iron  from  the 
stamps,  when  treated  in  the  pans  with  the  addition  of 
sulphate,  protochloride,  or  chloride  of  iron,  always  pro- 
duces amalgam  free  of  iron.  At  the  moment  of  amal- 
gamation, the  iron  is  in  metallic  condition,  and  also  after 
retorting,  but  when  the  retort  is  opened  and  the  air 
comes  in  contact  with  it,  the  amalgam  assumes  a  higher 
glow,  and  continues  so  for  twenty-four  hours.  During 
this  time,  most  of  the  iron  will  oxydize,  and  still  be 
attracted  by  the  magnet. 

It  is,  however,  very  likely  that  by  proper  roasting,  of 
a  reasonable  charge,  this  singular  appearance  can  be 
avoided. 

As  a  matter  of  course,  only  those  ores  or  tailings 
which  contain  a  sufficient  quantity  of  sulphurets,  espe- 
cially iron  sulphurets,  can  be  subjected  to  roasting. 
If  the  quantity  be  insufficient,  one  or  two  per  cent,  of 
calcined  green  vitriol  (sulphate  of  iron)  must  be  added, 
or  the  ore  must  be  concentrated,  saving  the  tailings  in 
the  usual  way.  The  concentrated  ore,  after  roasting, 
may  be  amalgamated  with  the  unroasted  tailings,  for 
which  the  roasted  part  represents  the  chemical. 


110  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

It  is  advisable  to  use  not  less  than  four  per  cent,  of 
salt,  and  not  to  charge  more  than  1,000  pounds  at  a 
time,  except  in  a  mechanical  furnace.  The  temperature 
must  be  kept  at  a  dark  red  heat  for  at  least  two  hours, 
and  one  hour  light  red  hot,  in  which  time  the  roasting 
of  1,000  pounds  of  ore  may  be  generally  completed. 
In  using  dry  ore,  the  formation  of  lumps  is  moderate, 
and  requires  no  sifting  or  grinding,  especially  if  Wheel- 
er's pans  are  used.  I  have  made  different  experiments 
with  roasted  ore  in  the  pans,  always  obtaining  the  best 
results  and  clean  amalgam,  except  in  one  instance,  pur- 
posely applying  a  very  low  temperature,  on  which  occa- 
sion, the  amalgam,  apparently  pure,  turned  black  after 
retorting,  and  consisted  mostly  of  iron. 

But  when  the  ore  contains  a  great  deal  of  copper  and 
other  base  metals,  the  roasting  must  be  treated  more 
carefully  (Sec.  33).  The  result  of  this  manipulation  is 
a  metal  more  or  less  impure,  between  600  and  700  fine — 
that  is,  if  the  roasting  has  been  properly  conducted  and 
the  ore  not  overloaded  with  base  metals. 

C.    ROASTING  OF  SILVER  ORES 
Abounding  in  Antimony,  for  Pan  Amalgamation. 

Sec.  35.  Ores,  containing  an  abundance  of  antimony, 
like  that  of  the  Sheba  lode  (Sec.  16,  11  b'),  which  is 
rich  in  silver,  can  not  be  treated  in  pans  without  roast- 
ing.   This  ore  is  accompanied  by  sulphuret  of  zinc,  sul- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  Ill 

phuret  of  lead,  and  carbonate  of  lead.  The  carbonate  of 
lead  is  black,  somewhat  dull,  and  also  rich  in  silver. 

In  selecting  the  ore  for  this  purpose,  the  sulplmret  of 
lead  must  be  separated  as  much  as  possible.  Some  of 
the  gangue  should  be  left  in  the  sulphurets.  Quartz  or 
other  earthy  matter  prevents  the  baking  of  the  ore 
while  roasting. 

The  hot  furnace  is  charged  with  six  or  seven  hundred 
pounds  of  ore,  and  while  the  mass  is  kept  at  a  very  low 
temperature,  below  glowing  heat,  it  is  diligently  stirred. 
The  sulphurets  of  antimony  and  lead  fuse  at  a  dark  red 
heat,  and  if  they  were  fused,  the  roasting  would  be  most 
imperfect,  and  result  in  a  loss  of  silver.  Care  must  be 
taken  to  keep  the  temperature  low,  especially  when  the 
ore  is  rich  in  sulphuret  of  antimony.  The  oxydation  of 
the  sulphur  and  antimony  will  soon  commence.  White 
fumes  of  antimonous  acid  arise,  gradually  increasing,  a 
strong  odor  of  sulphurous  acid  is  emitted,  while  constant 
stirring  exposes  always  a  new  surface  of  the  ore  to  the 
oxydizing  air. 

As  soon  as  it  is  perceived  that  the  fumes  and  the 
formation  of  sulphurous  acid  decrease,  the  heat  must  be 
raised  gradually,  so  that  about  two  hours  after  the 
charge  the  ore  appears  red  hot.  Sulphates  of  lead  and 
zinc  and  some  sulphate  of  silver  will  be  formed  with 
the  increasing  heat,  also  antimonate  of  silver,  of  which 
only  a  small  part  may  be  changed  into  sulphate  of  sil- 
ver under  the  influence  of  the  limited  quantity  of  gas- 
eous sulphuric  acid.    This  acid  is  partly  disengaged 


112  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

from  the  sulphates  of  lead  and  zinc  under  the  increasing 
heat,  which  at  the  expiration  of  three  or  three  and  a 
half  hours  must  be  nearly  light  red.  At  this  time  sam- 
ples must  be  taken  from  the  furnace,  and  if  ascertained 
by  odor  that  none  or  not  much  sulphurous  acid  is  emit- 
ted, the  first  part  of  the  roasting  is  finished. 

During  this  period  a  great  deal  of  antimony  is  vola- 
tilized, as  antimonous  acid,  and  also  some  oxyds  of  lead 
and  zinc. 

One  part  of  the  antimonous  acid  combines  with  anti- 
monate,  which  is  not  volatile.  To  disengage  this,  as 
well  as  the  antimonate  of  silver,  the  roasting  must  be 
changed  into  a  chloriclizing  one.  For  this  purpose,  five 
per  cent,  of  salt,  in  a  fine  pulverized  condition,  is  thrown 
into  the  furnace  with  a  scoop,  in  such  a  way  as  to  scat- 
ter it  over  the  whole  surface  of  the  ore. 

Soon  after  the  ore  and  salt  are  mixed  by  the  usual 
stirring,  white  fumes  will  arise  again,  consisting  chiefly 
of  chloride  of  antimony  which  is  very  volatile.  Also 
some  chloride  of  lead  and  zinc  are  volatilized.  The  sul- 
i  phate  of  silver  is  changed  into  a  chloride,  partly  by  the 
decomposition  of  salt,  partly  by  the  volatile  chlorine. 
The  formation  of  hydrochloric  acid  is  here  important  to 
assist  the  decomposition  of  the  antimonate  of  silver,  for 
which  purpose  the  introduction  of  some  steam  in  the 
furnace,  under  a  pressure  of  three  or  four  pounds,  will 
render  good  service.  The  ore  increases  in  volume  a 
great  deal,  becoming  woolly,  changing  its  color  by  de- 
grees to  light  yellow.    After  the  addition  of  the  salt, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  113 

the  temperature  must  be  increased  a  little  to  a  light  red 
heat,  and  after  one  hour's  chloridizing  roasting,  the  pro- 
cess is  completed  and  the  ore  discharged. 

As  a  matter  of  course,  some  silver  is  lost,  as  the  chlo- 
rides of  lead,  and  zinc,  and  antimony  will  dispose  the 
chloride  of  silver  to  evaporate.  The  amalgamation  of 
this  ore  will  yield  a  metal,  containing  a  considerable 
amount  of  lead,  according  to  the  quantity  of  lead  in  the 
roasted  ore. 

Mr.  Sutro  has  used  a  very  simple  way  of  separating 
the  lead  amalgam  from  the  silver  amalgam.  It  is 
known  that  the  silver  amalgam,  which  is  obtained  in 
the  pan  amalgamation,  consists  of  small  regular  crystals 
which  are  suspended  in  the  quicksilver.  The  lead  amal- 
gam, on  the  contrary,  is  entirely  dissolved  in  the  quick- 
silver when  hot.  If,  therefore,  the  quicksilver  is  pressed 
through  a  cloth  while  hot,  the  dissolved  lead  amalgam 
is  found  in  the  quicksilver,  and  the  silver  amalgam  in  the 
cloth.  A  second  filtration  of  the  quicksilver  when  cold, 
gives  the  lead  amalgam.  The  lead  contains  three  or 
four  per  cent,  of  silver.  It  is,  however,  not  likely  that 
this  way  of  separation  would  answer  when  Wheeler's 
pans  are  in  use,  for  they  yield  a  finer  amalgam ;  besides, 
it  is  dangerous  to  handle  hot  quicksilver.  A  surer  and 
more  perfect  separation  of  lead  and  silver  is  effected  by 
refining.    (Sec.  47.) 

8 


114  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

D.    ROASTING  OF  SILVER  ORES 
In  a  Mechanical  Furnace. 

Sec.  36.  The  difference  between  roasting  in  a  com- 
mon and  a  mechanical  furnace  is  merely  a  difference  of 
mechanical  operation,  but  on  the  more  or  less  proper 
execution  of  the  mechanical  operation  depends  also  the 
chemical  result.  Gurlt,  in  his  remarks  on  the  new  pro- 
gress of  the  copper  process  in  England,  speaks  of  a 
mechanical  double  roasting  furnace  with  revolving  stir- 
rers, which  he  saw  at  the  Pembrey  Copperworks.  He 
says,  one  of  these  double  furnaces  roasts  twenty-four 
tons  of  ore  in  twenty-four  hours,  and  recommends  it 
highly  for  roasting  copper  and  lead  ores,  but  he  thinks 
it  would  not  answer  for  roasting  where  a  great  deal  of 
attention  is  required,  for  instance  in  roasting  silver  ore. 
This  remark  may  be  true  in  Europe,  but  we,  in  Nevada 
Territory,  are  differently  situated.  In  Germany  the 
roaster  works  with  hands  and  head,  and  is  responsible 
for  the  result.  His  work  can  be  trusted.  Our  roasters 
are  inexperienced,  frequently  green  hands,  without  the 
least  interest  in  the  result.  A  good  mechanical  furnace 
is  also  reliable  in  its  performance,  and  responsible  for 
the  result. 

The  mechanical  furnace  which  I  propose  is  not  in  use 
to  my  knowledge,  but  it  may  be  easily  perceived  that 
no  other  furnace  offers  the  same  advantage  of  having 
the  ore  so  uniformly  heated.    Whatever  the  construe- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  115 

tion  of  the  roof  or  arch  of  a  furnace  may  be,  the  heat 
will  always  be  more  intense  at  the  bridge  than  on  the 
opposite  side.  This  requires  the  troublesome  moving 
of  ore  from  the  bridge  to  the  flue  and  back,  and  even 
then  the  disadvantage  of  the  .difference  in  temperature 
is  not  entirely  corrected.  The  revolving  bottom  of  the 
furnace  (Sec.  54,  Fig.  31)  carries  the  ore  at  each  revolu- 
tion through  all  the  different  temperatures  of  the  fur- 
nace, and  the  ore  is  twice  stirred,  thus  effecting  a  very 
uniform  heating  of  the  ore  and  consequently  also  a 
uniform  chemical  action. 

Such  a  furnace  will  roast  the  ore  with  much  more 
precision  than  a  common  furnace  attended  by  such 
roasters  as  we  can  get  in  Nevada  Territory,  and  it 
requires  on  that  account  less  time.  One  man  can 
attend  several  furnaces.  The  consumption  of  wood  will 
be  less  \  and  no  cooling  at  the  working  door  can  take 
place  as  in  other  furnaces  where  the  door  must  be  con- 
stantly open,  whereby  a  great  mass  of  cold  air  is  drawn 
in,  diminishing  the  draft  at  the  fire  place.  The  expenses 
are  thus  considerably  reduced,  but  the  most  important 
advantage  lies  in  the  more  perfect  roasting  which  gives 
a  better  result  in  extracting  the  silver. 

LOSS  OF  SILVER 
In  Roasting  Different  Silver  Ores. 

Sec  37.  In  roasting  the  ore  by  the  oxydation  method 
without  salt,  the  per  centage  of  loss  of  silver  will  be 


116  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

higher,  when  there  is  a  great  deal  of  metallic  silver  in 
the  ore,  or  when  it  is  produced  during  the  roasting,  or 
when  the  mass  of  ore  assumes  a  loose  condition,  admit- 
ting the  air  to  permeate  it.  The  loss  increases  also 
when  the  richness  of  the  ore  decreases,  or  when  for 
some  reason  the  temperature  must  be  kept  high.  The 
sulphate  of  silver  in  contact  with  the  oxyds  of  other 
metals  suffers  a  greater  loss  than  arsenate  or  antimony 
of  silver,  because  the  sulphate  is  more  easily  decomposed 
by  oxyds  at  a  high  temperature  and  reduced  to  the 
metallic  state.  In  roasting  the  ore  without  salt,  silver 
is  not  only  lost  mechanically,  being  carried  out  with  the 
draft,  but  chiefly  chemically  by  the  conversion  of  the 
metal  into  the  oxyd  of  silver,  which  is  volatile.  If  not 
combined  with  antimony,  it  deposits  itself  in  a  metallic 
form,  for  it  leaves  its  affinity  for  oxygen  at  a  lower 
temperature. 

At  Mansfeld,  where  Ziervogel's  method  is  practiced, 
in  extracting  silver  from  copper  matt  the  loss  of  silver, 
according  to  the  recent  accounts  of  Dr.  Heinbeck,  is  7*06 
per  cent,  in  roasting  and  1*20  in  extracting  the  silver, 
making  the  total  loss  of  8-26  per  cent.  This  is  consider- 
ed a  very  flattering  result.  Taking  into  account  the 
stuff  collected  from  the  dust  chambers,  the  loss  will  be 
diminished  somewhat. 

In  the  chloridizing  roasting,  if  properly  conducted 
and  if  there  are  no  base  metals  in  the  ore,  the  loss  of 
silver  is  less  than  in  the  oxydizing  roasting.  However, 
the  circumstances  which  determine  the  loss  are  different 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  117 

and  numerous,  but  generally  speaking  the  loss  by  roast- 
ing is  between  five  and  fifteen  per  cent.  Losses  above 
fifteen  or  below  five  per  cent,  are  exceptions. 

The  base  metal  ore  of  the  Ophir's  northern  claim  on 
the  Comstock  lode,  containing  lead,  zinc,  iron,  copper, 
and  antimony,  which  I  treated  for  the  barrel  amalgama- 
tion, mixing  it  with  fifty  per  cent,  of  pure  ore  (the 
latter  is  now  worked  by  itself),  after  having  been  care- 
fully roasted,  suffered  a  loss  of  between  five  and  eight 
per  cent,  of  silver.  The  accounts  of  the  present  losses 
in  some  works  where  roasting  is  going  on  are  consider- 
ed so  low,  that,  allowing  one  or  two  per  cent,  for  the 
amalgamation,  there  is  hardly  anything  left  for  loss  in 
roasting.  This  is  evidently  a  mistake,  founded  on  an 
improper  mode  of  taking  samples  for  that  purpose. 

AMALGAMATION  OF  ROASTED  ORE. 
a  Barrel  Amalgamation. 

Sec.  38.  The  amalgamation  in  barrels  is  not  adapted 
to  ore  containing  gold.  Unroasted  ore  has  been  tried 
with  chemicals  unsuccessfully.  The  construction  of  the 
barrels  does  nor  differ  much  in  the  different  works  of 
Nevada  Territory.  They  have  a  cylindrical  shape,  the 
diameter  and  depth  being  nearly  equal.  The  staves 
are  three  to  four  inches  thick.  There  are  two  sizes  in 
use.  The  smallest  capable  of  receiving  from  1,000  to 
1,300  pounds  of  ore,  are  thirty -two  inches  each  way; 
the  larger,  receiving  a  ton  of  ore,  measure  from  forty- 


118  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

four  to  forty-eight  inches  in  the  clear.  The  motion  is 
imparted  by  cog-wheels  although  belts  fitted  directly  on 
the  barrel  are  preferable.  The  stoppage  and  starting  by 
means  of  tightening  pullies  is  more  easily  effected  with- 
out jar. 

Above  each  barrel  is  a  wooden  or  sheet  iron  funnel, 
large  enough  to  receive  one  charge.  By  means  of  a 
hose,  fastened  at  the  mouth  of  the  funnel,  the  barrel  is 
charged  with  the  required  quantity  of  ore  in  a  short 
time.  When  this  is  done,  from  one  hundred  and  sixty 
to  two  hundred  pounds  of  wrought  iron  are  introduced. 
The  iron  is  in  pieces  of  different  shape  and  length,  but 
pieces  over  five  pounds,  and  such  as  have  rough  and 
sharp  edges  and  ends,  wear  the  staves  too  much.  After 
the  iron,  cold  water  is  added  in  such  a  proportion  as  to 
form  a  thickish  paste.  One  ton  of  ore  may  require  five 
hundred  or  six  hundred  pounds  of  water,  according  to 
the  fineness  of  the  ore. 

The  barrel  is  then  closed  tightly  and  set  in  motion, 
at  the  speed  of  about  twelve  revolutions  per  minute. 
After  two  hours'  run,  the  barrels  are  stopped  and  exam- 
ined. By  this  time  the  mass  of  ore  should  be  of  such 
consistency  as  to  allow  the  forming  of  a  soft  ball  with 
the  hand.  If  the  pulp  adheres  to  the  hand  and  fingers 
so  that  no  ball  can  be  formed,  some  thirty  or  fifty 
pounds  of  ore  may  be  added,  but  if,  on  the  contrary, 
the  stuff  is  so  dry  that  it  crumbles  into  pieces,  some 
more  water  must  be  added.  After  the  ore  has  been 
found  to  be  in  the  right  condition,  the  barrels  are 


PROCESSES  OF  SILVER  AXD  GOLD  EXTRACTION.  119 

charged  with  quicksilver.  One  thousand  pounds  of  ore 
require  five  hundred  pounds  of  quicksilver.  The  open- 
ing is  closed  again  and  secured  by  means  of  a  screw. 
The  motion  must  be  changed  now  to  eighteen  or  twenty 
revolutions  per  minute. 

Four  hours  after  the  quicksilver  has  been  charged, 
each  barrel  must  be  examined  again.  For  this  purpose 
the  barrel  is  stopped  and  opened.  A  wooden  stick, 
about  an  inch  thick,  is  dipped  into  the  pulp  and  with- 
drawn. If  the  ore  is  so  diluted  that  it  runs  down  from 
the  stick,  forming  a  long  thread,  the  quicksilver  and  the 
iron  sink  to  the  bottom,  the  amalgamation  is  imperfect, 
and  the  iron  does  useless  damage  to  the  barrel.  Some 
dry  ore  may  be  added,  but  after  this  time  no  more.  If. 
on  the  other  hand,  the  ore  crumbles  from  the  stick,  or  if 
it  is  so  stiff  that  it  does  not  adhere  at  all,  the  suspended 
quicksilver  and  iron  have  no  chance  to  change  their 
places,  and  the  amalgamation  will  give  a  very  poor  re- 
sult. An  addition  of  water  is  therefore  in  this  case 
necessary.  The  barrels  are  put  in  motion  again  and 
continued  for  fourteen  hours,  so  that  the  period  of  amal- 
gamation, from  the  introduction  of  quicksilver,  will  last 
about  eighteen  hours,  after  which  the  barrels  are  filled 
with  water,  set  in  motion  at  a  reduced  speed,  and  after 
one  or  two  hours  run,  discharged. 

The  discharge  is  performed  in  different  ways.  Oppo- 
site the  feedhole  in  the  barrel  is  a  small  hole,  shut  by 
an  inch  screw.  Through  this  hole  the  quicksilver  is  let 
out  first,  directly  into  the  filter  or  into  a  common  re- 


120  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

ceiver.  As  soon  as  the  mud  appears,  the  screw  is  put 
in,  the  plug  of  the  feedhole  removed,  the  barrel  turned 
over,  and  the  tailings  discharged  into  a  large  inclined 
trough  below  the  barrels,  leading  into  agitators,  where 
the  tailings  are  diluted  with  more  water,  in  order  to 
allow  the  settling  of  the  particles  of  quicksilver  and 
amalgam,  requiring  five  or  six  hours,  when  the  tailings 
are  discharged.  The  contents  of  the  barrels,  quicksil- 
ver and  tailings  are  also  discharged  at  once  into  the 
agitators,  the  bottoms  of  which  have  a  conical  shape, 
like  Wheeler's  agitator.    (See  Sec.  51,  Fig.  26.) 

The  agitator  is  a  tub,  five  or  six  feet  in  diameter,  and 
about  the  same  in  height.  On  the  perpendicular  centre- 
shaft  are  four  arms  with  staves,  three  or  four  inches 
apart,  performing  the  stirring.  The  shaft  makes  twelve 
revolutions  per  minute.  In  Washoe  Valley  there  is  an 
agitator,  sixteen  feet  in  diameter.  This  size  can  not  be 
recommended.  The  purpose  of  the  agitator  is  to  have 
such  a  motion  and  such  a  dilution  that,  while  the  earthy 
particles  are  kept  in  suspension,  the  heavier  but  minute 
particles  of  quicksilver  can  sink  by  degrees  to  the  bot- 
tom. If  the  mass  is  too  thick,  the  quicksilver  will  be 
kept  suspended;  if  it  is  too  diluted,  the  sand  settles 
with  the  quicksilver.  The  former  result  will  also  occur, 
if  the  motion  is  too  fast,  and  the  latter,  if  the  motion  is 
too  slow.  A  sixteen  feet  agitator  has  a  tremendous 
speed  on  the  periphery  when  the  motion  near  the  cen- 
tre is  right.  Even  eight  feet  is  too  large,  unless  the 
agitator  is  not  intended  to  effect  a  perfect  separation, 
but  is  used  like  Wheeler's  agitator.    (See  Sec.  27.) 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  121 

As  soon  as  the  barrels  are  empty,  and  the  iron  pieces, 
which  may  happen  to  fall  out,  replaced,  the  charging  is 
performed  as  before.  The  quicksilver,  which  came  out 
of  the  barrels,  is  strained,  and  the  amalgam  retorted. 
(Sec.  42.) 

The  object  of  using  metallic  iron  in  the  barrel  is  to 
decompose  the  sesquichloride,  or  chloride  of  iron,  and 
to  reduce  it  to  protochloride.  The  chlorides  of  silver, 
copper,  and  lead,  as  well  as  some  sulphates,  after  hav- 
ing been  reduced  to  the  metallic  state,  combine  with 
the  quicksilver,  which  is  introduced  after  all  these  reac- 
tions have  been  effected  by  the  metallic  iron.  In  the 
absence  of  iron  these  chlorides  would  be  decomposed 
by  the  quicksilver,  which,  forming  sub-chloride  of  quick- 
silver, would  decompose  no  longer,  causing  a  great  loss 
in  mercury,  and  the  amalgamation  would  be  imperfect. 

Metallic  copper,  in  place  of  iron,  acts  with  little  less 
energy  than  the  iron,  but,  not  reducing  the  copper  and 
lead  chlorides  to  the  metallic  state,  it  renders  a  very 
pure  amalgam.  It  is  by  no  means  necessary  to  use  pure 
copper  in  the  barrels.  In  treating  the  copperous  silver 
ore  from  the  Heintzelman  mine  in  Arizona,  I  was  obliged 
to  procure  copper  by  liquation  of  copperous  lead.  Be- 
ing limited  in  regard  to  heat,  for  want  of  firebrick, 
the  copper  could  not  be  refined  properly,  having  a 
grayish  red  color,  on  account  of  some  lead.  This  cop- 
per, as  well  as  black  copper,  bought  from  Mexicans, 
gave  a  very  favorable  result  as  to  the  quality  and  quan- 
tity of  the  silver  extracted. 


122  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

b.  Amalgamation  in  Dr.  Veatch's  Steam  Tubs. 

Sec.  39.  The  principle  of  this  amalgamation,  which  is 
performed  at  the  Central  Works  (Virginia  City)  is,  in 
regard  to  chemical  procedure,  the  same  as  that  of  the 
barrel  amalgamation.  Chlorides  and  sulphates  are  de- 
composed by  wrought  iron  or  copper  plates.  But,  while 
the  barrels  discharge  the  quicksilver  after  each  amalga- 
mation of  a  new  charge,  in  order  to  save  it  from  destruc- 
tion by  decomposition,  the  steam  tubs  retain  it  for  many 
charges,  according  to  the  richness  of  the  ore.  The 
quicksilver  therefore  takes  an  active  part  in  decompos- 
ing the  chlorides,  forming  calomel.  In  this  combination 
the  quicksilver  is  always  lost.  The  steam  has  no  chemi- 
cal action,  but  it  may  influence  the  amalgamation  by 
its  temperature.  In  regard  to  the  mechanical  part  of 
amalgamation,  these  tubs  differ  entirely  from  the  barrel 
arrangement.  There  are  wooden  tubs  about  four  feet 
deep  and  four  feet  in  diameter.  The  bottom  is  made  of 
cast  iron  with  three  circular  openings  for  the  reception 
of  perforated  plates,  also  of  cast  iron,  below  which  are 
the  steam  chambers.  The  holes  are  very  fine,  about  two 
inches  apart.  In  the  middle  of  the  tub  is  an  upright 
shaft,  suspended  on  a  box  outside  of  the  tub.  There 
are  three  arms  attached  to  it,  each  having  three  copper 
or  iron  plates  hanging  perpendicularly  in  concentric 
lines.  The  movable  cover  has  an  opening  in  connection 
with  a  flue  by  which  the  steam  and  some  quicksilver 
are  carried  into  cooling  tanks. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  123 

The  steam  is  forced  through  the  perforated  plates 
into  the  pulp,  throwing  the  quicksilver  in  globules  of 
all  sizes  constantly  through  the  whole  mass,  causing  a 
very  perfect  contact  between  the  ore  and  mercury. 
The  iron  plates — or  if  the  ore  is  very  copperous,  copper 
plates,  — nine  in  number,  have  a  circular  motion,  cut  the 
ore  with  the  edge,  require  very  little  power,  and  assist 
the  motion  of  the  pulp.  The  decomposition  of  chlorides 
goes  on  very  rapidly  in  consequence  of  the  heat  and 
contact  with  the  plates,  which  expose  about  3,600 
square  inches  of  surface  to  a  mass  of  six  or  eight 
hundred  pounds  of  ore.  Under  such  circumstances  the 
amalgamation  may  be  effected  in  five  hours,  but  as  a 
matter  of  course,  the  result  depends  entirely  on  a 
proper  roasting.  With  regard  to  saving  the  gold  in 
silver  ore,  this  amalgamation  may  be  equal  to  that  of 
the  barrels.  Gold  requires  friction,  silver  chemical 
action.  I  could  not  ascertain  the  loss  of  quicksilver, 
but  very  likely  it  must  be  greater  than  in  the  barrel 
amalgamation,  not  only  on  account  of  being  converted 
into  calomel  to  some  extent,  but  also  by  being  dispersed 
by  the  force  of  steam,  which  should  for  that  reason  be 
carefully  regulated.  The  mechanical  loss  and  that  by 
evaporation,  in  consequence  of  considerable  heat  in  the 
tubs,  is  not  important,  as  the  greater  part  of  the  quick- 
silver is  condensed  in  a  cooling  tank. 

This  amalgamation  is  superior  to  barrel  amalgama- 
tion in  regard  to  the  time  and  the  amount  of  power 
required,  still  there  are  some  inconveniences  which 


124  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

have  not  yet  been  removed.  The  choking  of  the  fine 
holes  in  the  perforated  plates  by  amalgam,  the  cleaning 
of  which  is  troublesome,  might  be  avoided  by  discharg- 
ing the  quicksilver  after  each  amalgamation ;  but  then 
the  plates  would  come  too  much  in  contact  with  the 
different  salts  of  the  ore,  which  doubtless  would  enlarge 
the  holes  and  cause  more  damage  than  benefit.  The 
cleaning  of  the  tubs  is  injurious  to  the  health  of  the 
workmen,  if  no  time  is  allowed  for  cooling  or  precipita- 
tion of  the  vapor  of  the  mercury. 

The  roasted  and  finely  pulverized  ore  is  spread  on  a 
platform  moistened  with  water,  and,  after  the  plates 
have  been  set  in  motion,  the  quicksilver,  water,  and 
some  steam  introduced.  The  amalgamator  is  charged 
with  six  or  eight  pounds  of  ore  by  means  of  a  shovel. 
If  there  is  too  much  steam,  the  ore  will  be  thrown  up 
with  the  quicksilver  against  the  cover,  if  on  the  other 
hand  the  steam  has  too  little  force,  the  amalgamation  is 
delayed.  The  amalgam  deposits  partly  on  the  plates, 
where  it  must  be  removed  by  iron  scratchers  without 
taking  out  the  plates.  After  four  or  six  hours,  accord- 
ing to  the  richness  of  the  ore,  the  amalgamators  are 
discharged  into  agitators. 

c.  Amalgamation  in  Pans. 

Sec.  40.  Ores  containing  such  compounds  of  silver  as 
cannot  be  treated  satisfactorily  in  pans,  or  concentrated 
tailings  of  the  pan  amalgamation,  which  contain  chiefly 
such  silver  ore  as  has  resisted  the  action  of  chemicals, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


125 


will  give  the  best  result  after  having  been  subjected  to  a 
chloridizing  roasting.  The  presence  of  base  metals  will 
of  course  render  the  amalgam  impure,  but  this  depends 
partly  on  the  greater  or  less  attention  given  to  the 
roasting.  A  certain  amount  of  copper  in  the  bar  is  not 
so  injurious  after  all,  increasing  only  the  expense  for 
transportation  by  express. 

If  the  ore  is  of  such  a  nature  that  a  great  deal  of 
lead  enters  the  amalgam,  the  metal  must  be  refined, 
and  in  this  case  the  calculation  will  show  whether  there 
is  more  economy  in  working  the  ore  without  roasting, 
even  if  more  silver  be  lost.  Generally,  if  in  treating 
ore  of  about  one  hundred  ounces  per  ton  by  means  of 
roasting,  not  more  than  ten  per  cent,  of  silver  were 
saved,  it  would  not  pay  to  roast.  If  the  ore  is  very 
rich,  especially  when  there  is  also  gold  in  it,  the  proper 
way  of  reducing  it,  is  to  amalgamate  it  in  pans  without 
roasting,  save  the  tailings  in  large  tanks,  roast  them 
subsequently  and  work  them  over  in  pans,  either  alone 
or  mixed  with  raw  ore.  In  this  case,  although  the 
water  always  carries  off  some  ore  in  form  of  the 
finest  slime,  yet  the  loss  is  less,  or  may  be  a  great  deal 
less,  than  the  loss  in  roasting  some  qualities  of  rich  ore. 
We  must  take  into  consideration  the  fact  that  if  the 
rich  ore  be  treated  by  roasting  previous  to  amalgama- 
tion, it  must  suffer  not  only  the  chemical  loss  but  also 
that  caused  by  the  draft  of  the  furnace ;  whereas  the 
tailings,  when  exposed  to  the  furnace  after  amalgama- 
tion, will  have  only  the  sixth  part  or  so  of  the  value  of 
the  original  ore. 


126  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Ores  containing  antimony  to  excess,  like  that  of  the 
Sheba  lode  (in  Humboldt  County,  N.  T.),  or  combina- 
tions with  zinc  and  iron,  like  the  ore  from  the  Rappa- 
hannock lode  (Palmyra  District,  N.  T.),  cannot  be  treat- 
ed in  pans  without  roasting ;  also,  auriferous  arsenical 
or  iron  pyrites  require  roasting. 

The  amalgamation  can  be  executed  in  different  pans ; 
but  in  order  to  save  quicksilver  from  being  changed 
into  subchloride,  the  arrangement  must  be  made  that 
after  each  charge  tailings  and  quicksilver  be  discharged. 
The  construction  of  Wheeler's  and  Hepburn's  pans 
makes  such  discharge  necessary.  On  this  account,  and 
because  they  are  superior  in  many  respects,  they  are 
preferable  to  other  pans.  But  the  dies  in  Wheeler's 
pans  form  curved  grooves  in  which  a  part  of  the  quick- 
silver and  amalgam  remains  after  the  discharge.  They 
must  be  replaced  by  a  bottom  of  one  piece  of  hard  iron 
or  dies  without  space  between  them. 

The  ore  is  then  introduced  according  to  the  ca- 
pacity of  the  pan  and  the  volume  of  the  ore ;  for 
instance,  five  or  six  hundred  pounds  into  one  Wheeler's 
pan,  or  ten  hundred  pounds  into  Hepburn's,  with  a 
sufficient  addition  of  water.  The  steam  must  be  used 
moderately.  The  ore  undergoes  now  the  same  process 
as  in  the  barrels.  After  one  hour's  time,  when  the  most 
of  the  chlorides  and  sulphates  are  decomposed  and  the 
silver  reduced  to  the  metallic  state,  sixty  pounds  of 
quicksilver  are  introduced.  The  amalgamation  now 
goes  on  with  the  same  speed  and  moderate  temperature 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  127 

for  two  hours.  Then  all  is  discharged.  The  pan  is 
charged  again,  and  the  procedure  is  the  same  as  before. 
Wheeler's  and  Hepburn's  pans  alike  require  about  three 
hours  for  the  amalgamation  of  a  charge.  Others  may 
require  four  or  five  hours,  according  to  their  service- 
ableness. 

If  the  ore  renders  an  impure  amalgam,  the  impurity 
can  be  best  ascertained  after  the  first  discharge  by 
taking  a  sample  of  about  ten  grains  of  amalgam,  which 
is  heated  to  red  heat  by  fire  under  draft,  in  order  to 
get  rid  of  quicksilver.  This  sample  thus  retorted  must 
be  examined  under  the  blowpipe  (see  Sec.  11).  If  there 
are  no  other  metals  in  it  but  iron,  there  is  no  remedy 
save  better  roasting.  The  chlorides  of  other  base 
metals  can  be  destroyed  by  using  some  quicklime,  pul- 
verized lime  rock,  or  clean  wood  ashes.  One  or  one 
and  a  half  per  cent,  of  lime  is  charged  with  the  ore. 
After  a  quarter  of  an  hour's  time,  a  small  portion  of  the 
ore  is  taken  from  the  pan,  put  into  a  porcelain  cup,  and, 
by  means  of  a  piece  of  copper,  stirred  with  some  water 
and  a  few  drops  of  quicksilver.  If  the  quicksilver  be 
covered  with  a  black  coat  instantly,  some  more  lime 
must  be  added.  Fifteen  minutes  later  another  sample 
is  taken  in  the  same  way,  and  so  on  till  the  quicksilver 
does  not  appear  black,  or  very  slightly  so.  Too  much 
lime  is  injurious  to  the  extraction  of  silver. 

This  method  is  only  a  temporary  remedy.  It  can  be 
better  executed  in  the  furnace.  Such  ore,  introduced 
with  about  fifty  per  cent,  of  raw  ore  may  prove  a  very 
good  chemical. 


128  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 


in.    COLD  PROCESS. 

AMERICAN  HEAP  AMALGAMATION  OR  PATIO. 

Sec.  41.  The  patio  amalgamation,  where  wood  and 
water  are  scarce,  the  ore  suitable,  the  climate  favorable, 
and  labor  cheap,  is  a  very  good  process,  and  in  many 
cases  cannot  be  replaced  by  a  better  one.  The  climate 
of  Nevada  Territory,  at  least  in  the  summer,  is  very 
favorable  for  the  patio ;  but  several  months  of  the 
winter  time  do  not  permit  this  process,  without  having 
proper  buildings,  in  which,  by  the  aid  of  steam  and 
other  arrangements,  the  required  temperature  is  obtain- 
ed, although  the  sunbeams  and  open  air  assist  the 
process,  independent  of  the  temperature.  On  the  other 
hand,  there  are  the  disadvantages  that  the  expenses  of 
steam  power,  horses,  and  men  are  comparatively  much 
heavier  here  in  Nevada  Territory,  than  for  instance  in 
Mexico  or  South  America.  Besides,  it  is  hardly  possible 
that  this  process  should  justify  its  use,  along  side  of 
pans  working  three  or  four  tons  of  ore  in  twenty-four 
hours,  with  less  expense  and  similar  or  better  results, 
according  to  the  nature  of  the  ore. 

Ores  containing  gold  cannot  be  treated  by  patio, 
unless  that  metal  is  extracted  first  in  some  other  way. 

The  best  and  at  the  same  time  cheapest  method  is  to 
extract  gold  by  the  new  improved  pans,  offering  also 
the  advantage  of  the  finest  grinding,  required  for  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  129 


patio,  but  in  this  case  the  tailings  of  poorer  ore  would 
not  pay  to  be  worked  over  by  the  patio  process. 

The  ores  most  suitable  for  this  process  are  Brittle- 
silver  ore,  Polybasite,  Rubysilver,  Bromyrite,  Iodyrite, 
Silverglance,  and  Chloride  of  Silver.  The  last  two,  on 
account  of  their  toughness  and  ductility,  amalgamate 
with  little  more  difficulty  than  the  other  compounds. 

Silver,  combined  with  copper  and  antimony,  must  be 
slightly  roasted  before  being  subjected  to  patio  amalga- 
mation. It  requires  generally  a  very  low,  dark  red 
heat,  being  stirred  only  at  intervals  for  about  twelve 
hours.  Such  ore  can  often  be  treated  without  magis- 
tral. If  similar  ore  be  taken  into  the  patio  without 
roasting,  it  remains  cold,  when  the  usual  quantity  of 
magistral  is  taken ;  and  an  abundance  of  it  does  not 
effect  a  proper  extraction  of  silver.  If  on  the  other 
hand  such  ores  are  roasted  too  much,  the  patio  appears 
very  hot.  It  is  well  to  let  it  rest  after  roasting  for  a 
few  clays  in  a  moist  condition. 

Argentiferous  zincblend,  pyrites,  and  some  other  com- 
binations cannot  be  treated  by  patio  without  a  perfect 
roasting.  Gold  ores  and  argentiferous  lead  ores  are 
entirely  excluded  from  this  process. 

The  patio  process  wTas  tried  in  Virginia  City,  and  is 
at  present  practiced  in  Washoe  Valley  and  on  Carson 
Biver.  The  theory  of  this  process  does  not  explain  the 
chemical  procedure  satisfactorily.  Salt  and  the  magis- 
tral, containing  about  eighty  per  cent,  of  sulphate  of 
copper,  prepared  from  copper  pyrites  by  roasting  at  a 
9 


130  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

moderate  temperature,  generally  with  an  addition  of 
salt,  are  the  two  agents,  acting  and  reacting  mutually 
on  each  other  and  on  the  sulphurets  in  the  presence 
of  quicksilver.  To  these  reactions  the  amalgamator 
(azognero)  gives  his  particular  attention  by  making  fre- 
quent tests  with  his  horn  spoon  or  other  instrument. 
Notwithstanding  all  his  care,  it  is  sometimes  found 
necessary  to  add  to  the  mass  a  portion  of  quick  lime, 
little  or  much,  as  the  case  may  require,  for  the  purpose 
of  counteracting  the  injurious  effects  of  too  much  magis- 
tral. The  blue  vitriol  in  place  of  magistral  is  less  fit  on 
account  of  its  vigorous  action  upon  the  quicksilver. 

The  loss  of  quicksilver  occurs  here,  as  in  other  opera- 
tions, for  two  reasons:  the  chemical,  or  "consume,"  and 
the  mechanical,  or  "loss."  The  chemical  is  almost  inva- 
riably equal  to  the  weight  of  the  silver  extracted.  The 
mechanical  depends  on  the  attention  and  ability  of  the 
amalgamator. 

The  ore  is  first  ground  very  fine ;  then  from  thirty  to 
sixty  tons  are  laid  out  on  the  floor  (patio)  and  mixed 
well  with  some  water  to  a  proper  consistency.  Samples 
are  taken  from  all  parts  of  the  mass,  a  fire  assay  is  made 
of  them,  and  salt  is  introduced,  amounting  to  two  or 
four  per  cent,  according  to  the  quality  of  the  salt  and 
the  quality  of  the  ore.  An  excess  of  salt  does  not  in- 
jure the  operation.  When  the  salt  is  well  mixed  with 
the  mass,  it  should  remain  undisturbed  for  one  or  two 
days  to  permit  the  salt  to  be  dissolved.  The  mass  is 
then  turned  over  and  worked,  by  treading  with  horses 
or  other  means,  to  a  uniform  proper  consistence. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  131 

The  magistral  is  then  incorporated,  about  one  per 
cent,,  more  or  less,  according  to  the  quality  of  the  ore, 
the  temperature,  and  the  situation.  After  the  magis- 
tral has  been  well  tramped  in,  the  quicksilver  is  next 
scattered  over  it  by  straining  through  canvass.  The 
amount  of  quicksilver  first  introduced  is  from  one-half 
to  two-thirds  of  the  whole  that  may  be  required,  which 
is  about  six  pounds  to  one  pound  of  silver,  as  ascer- 
tained by  the  assay  of  the  sample. 

After  some  days,  the  first  part  of  the  quicksilver  has 
combined  with  enough  silver  to  form  a  dry  amalgam. 
When  this  is  the  case,  one-half  of  the  remainder  of  the 
quicksilver  is  added,  mixed  and  trodden  as  before,  and 
when  after  several  days  it  is  discovered  that  there  is 
again  dry  amalgam,  the  last  part  of  the  mercury  is  in- 
troduced. Some  days  later,  the  amalgamation  is  fin- 
ished, and  then  some  more  quicksilver  may  be  added 
for  the  purpose  of  washing  more  easily. 

The  Torta  (mass  of  the  pulp)  is  tested  twice  a  day 
by  taking  a  small  quantity  of  the  pulp  from  different 
parts  of  the  torta,  and  carefully  washing  it  in  a  horn- 
spoon.  The  mud  is  washed  away,  leaving  the  amalgam 
on  the  bottom,  also  undecomposed  sulphurets,  and  sil- 
ver partially  combined  with  minute  particles  of  quick- 
silver {limadura).  This  Umadura  is  separated  from  the 
other  parts  by  a  peculiar  shaking  of  the  spoon,  and  be- 
comes the  principal  object  for  the  azoguero's  inspection. 
By  its  various  states  and  color,  the  process  of  the  patio 
is  understood.    There  are,  however,  so  many  variations 


132  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

of  appearance,  that  it  requires  a  great  deal  of  experi- 
ence to  form  a  correct  judgment. 

In  the  absence  of  magistral,  for  want  of  copper 
pyrites,  blue  vitriol  or  sulphate  of  copper  is  substituted. 
Mr.  W.  M.  Brown,  an  experienced  practical  azoguero, 
who  managed  the  patio  operation  at  the  Mexican  mill, 
Virginia  City,  and  afterwards  on  Carson  Eiver,  prepares 
his  magistral  by  roasting  pan-tailings  at  a  proper  tem- 
perature, they  containing  a  certain  proportion  of  salt. 
These  roasted  tailings  are  mixed  with  the  ore  and  act 
upon  it  as  magistral. 

RETORTING. 

Sec.  42.  The  amalgam,  a  combination  of  gold  and 
silver  with  mercury,  must  be  separated,  for  the  purpose 
of  having  the  metal  prepared  for  melting,  also  to  regain 
the  quicksilver  for  further  use.  The  separation  is  called 
"retorting"  a  very  simple  process,  being  a  mere  distilla- 
tion at  a  high  heat.  The  quicksilver  assumes  a  gaseous 
form,  is  led  off  through  a  cold  pipe,  and  is  condensed 
again  to  the  metallic  state,  while  the  other  metals  re- 
main in  the  retort. 

The  retorts  used  in  Nevada  Territory  differ  very 
much  in  shape  and  size.  Those  having  an  oval  or  cylin- 
drical form  are  better  than  flat-bottomed  retorts,  which 
always  require  a  separate  trough  for  the  amalgam,  on 
account  of  the  obstructive  corners ;  besides,  they  have 
the  disadvantage  of  being  more  liable  to  burst.  The 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  133 

retort  most  used  at  present  is  the  cylindrical  retort. 
(Sec.  55,  Figs.  20,  21.)  The  egg  retort,  of  an  oval 
shape,  but  lately  introduced,  seems  to  permit  a  more 
convenient  charging  and  saving  of  fuel.  This  retort 
contains  movable  troughs  or  shelves  for  the  amalgam. 

Before  charging,  the  lower  part  of  the  cylindrical 
retort  must  be  coated  with  a  soft  pulp  of  fine,  sifted 
wood  ashes,  by  means  of  a  long  rod,  to  one  end  of 
which  a  rag  is  tied.  The  same  precaution  must  be  ob- 
served with  the  troughs  for  the  egg  retort.  When  dry, 
the  amalgam  is  introduced  into  the  retort  in  balls  or 
pieces.  Sufficient  room  at  the  top  must  be  left  for  the 
vapors  of  quicksilver.  If  overcharged,  some  amalgam 
may  come  out  at  the  pipe-hole.  A  retort  of  the  size  as 
described  in  Sec.  55  should  not  be  charged  with  more 
than  eight  hundred  or  nine  hundred  and  fifty  pounds  of 
silver  amalgam. 

When  filled,  the  retort  must  be  closed  carefully,  so 
that  no  vapors  of  quicksilver  can  escape  anywhere. 
For  this  purpose  the  face  of  the  door  is  covered  with  a 
paste  of  pure,  fine,  sifted  ashes,  about  half  an  inch  thick. 
The  paste  should  be  soft,  but  must  not  run.  The  cor- 
respondent face  of  the  retort  is  moistened,  and  the  door 
set  in,  fastened  by  the  two  wedges  and  tapped  with  a 
wooden  mallet.  No  force  at  all  is  required.  If  the  ash 
paste  has  the  right  consistency,  the  closing  will  be  per- 
fectly tight. 

When  this  is  done,  the  fire  can  be  started  imme- 
diately.   As  soon  as  the  water,  which  cools  the  pipe. 


134  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

commences  to  boil,  the  fire  must  be  kept  very  moderate 
for  some  hours,  and  increased  when  the  boiling  goes 
down.  In  about  four  hours  after  beginning,  the  retort 
should  be  dark  red-hot,  and  kept  in  this  state  for  two  or 
three  hours  more,  when  the  heat  may  be  increased  a 
little,  not  allowing  a  good  light  red  heat,  which  would 
melt  the  silver  partly,  and  also  injure  the  retort. 

When  the  pipe  gets  cool,  and  no  quicksilver  drops 
out,  the  retorting  is  finished.  The  water  in  the  cooling 
pan,  covering  the  quicksilver,  must  be  clear.  If  it  be- 
comes milky,  the  distillation,  on  account  of  too  much 
heat,  was  too  sudden.  It  requires  eight  or  ten  hours  to 
drive  off  all  the  quicksilver.  A  forced  retorting  does 
not  gain  much  in  time ;  the  amalgam  will  generally  be 
found  not  well  retorted,  and  the  retort  will  be  used  up 
in  half  the  time.  It  is  not  the  shape  of  a  retort,  but 
the  time  that  is  important  for  a  good  retorting.  It  is 
also  a  bad  habit  to  open  the  retort  before  all  is  cooled 
down.  A  hot  retort,  even  after  the  best  retorting,  con- 
tains mercurial  vapors  which  are  very  injurious  to  the 
health,  although  the  influence  is  not  perceived  imme- 
diately. When  cold,  the  metal  is  taken  out  and  broken 
into  pieces  for  the  purpose  of  melting. 

MELTING  OF  RETORTED  METAL. 

Sec.  43.  The  retorted  metal  is  of  a  spongy  appear- 
ance, crumbling  easily,  and  on  that  account  is  not  fit  for 
transportation  or  handling.    To  prepare  it  for  transpor- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  135 

tation  and  to  ascertain  its  value  by  assay,  the  retorted 
metal  must  be  melted  into  bars. 

The  furnace  is  of  simple  construction  (Sec.  56,  Figs. 
13,  14),  square  or  round  on  the  inside,  and  from  ten  to 
fourteen  inches  in  the  clear,  according  to  the  size  of  the 
crucible.  The  best  are  the  black  lead  crucibles.  Before 
using,  they  require  to  be  annealed,  that  is,  heated  slowly 
by  degrees  to  red  heat.  This  may  be  performed  in  the 
same  furnace  on  a  moderate  charcoal  fire,  or  after  melt- 
ting,  when  the  heat  has  gone  down  somewhat.  The 
crucible  must  always  be  put  first  with  the  brim  on  the 
fire,  so  that  the  bottom  is  turned  upwards.  When  the 
brim  appears  red-hot,  the  crucible  can  be  turned  without 
danger  of  cracking. 

The  most  intense  heat  in  the  furnace  is  one  and  a 
half  or  two  inches  above  the  grate.  The  crucible,  there- 
fore, ought  to  stand  always  on  a  piece  of  fire-brick,  so 
as  not  to  be  exposed  to  the  cold  draft  of  the  air. 

When  the  crucible  is  placed  perpendicularly  in  the 
centre  and  covered,  the  charcoal  is  put  around  it  and 
on  and  over  the  cover,  some  live  coals  on  top,  and  the 
furnace  is  shut  by  the  slides.  When  the  crucible  ap- 
pears red-hot,  the  cover  is  removed  carefully,  that  no 
charcoal  falls  into  it,  and  so  much  silver  as  the  crucible 
will  hold  (from  twelve  to  twenty  pounds)  is  introduced 
with  a  pair  of  longhandled  tongs.  A  handful  of  borax 
is  also  added.  The  crucible  is  then  covered,  and  the 
furnace,  after  a  new  charge  of  charcoal,  closed  again. 
In  about  half  an  hour  the  silver  is  melted  down  so  far 


136  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

that  another  portion  of  silver  can  be  introduced,  and  so 
on,  till  fifty  or  sixty  pounds,  which  is  about  the  right 
amount  for  a  proper  bar,  are  melted  down. 

The  borax  must  be  used  in  proportion  to  the  impuri- 
ties of  the  metal.  If  the  retorted  metal  is  white  and 
clear,  one  handful  is  sufficient;  but  if  the  amalgam 
looks  black,  double  the  quantity  is  required.  The  borax 
dissolves  the  oxyds  of  base  metals  and  earthy  matters, 
which  may  happen  to  be  in  the  amalgam,  and  forms  a 
black  slag,  which  covers  the  metal.  Some  amalgama- 
tions furnish  amalgam,  containing  a  great  deal  of  sul- 
phurets.  When  melted,  the  sulphur  takes  up  so  much 
silver  as  to  form  a  combination  similar  to  the  silver- 
glance,  containing  eighty  per  cent,  of  silver.  If  there 
is  metallic  iron  in  the  amalgam  or  crucible,  it  combines 
with  the  sulphur,  setting  the  silver  free.  This  combina- 
tion of  sulphur  and  metals,  called  "matt,"  is  poorer  in 
silver,  in  proportion  to  the  amount  of  metallic  iron 
present.  The  matt  is  more  liquid  than  the  slag,  but 
heavier.  It  lies  on  the  metal,  below  the  slag.  If  rich 
in  silver,  the  matt  is  tough,  bluish  gray ;  if  poor,  it  is 
brittle  and  has  a  yellowish  gray  appearance. 

After  the  last  charge  is  melted,  the  cover  is  removed 
and  metal  and  slag  stirred  well  by  means  of  a  red-hot 
iron  rod,  then  covered,  and  a  good  heat  effected  by 
another  charge  of  charcoal,  when  the  slag  is  taken  oft 
This  is  generally  done  by  a  skimmer  (Fig.  16),  made  of 
half  inch  round  iron,  rolled  into  a  coil  at  one  end.  With 
this  skimmer  the  slag  is  touched  carefully,  not  dipping 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  137 

too  deep.  The  slag  adheres  to  the  skimmer,  which  is 
taken  out  immediately  after  it  comes  into  contact,  and 
tapped  slightly  against  the  stone  floor,  or  a  wet  board. 
With  this  cooled  coating  the  skimmer  is  clipped  again 
into  the  crucible,  and  the  adhering  slag  treated  as  before. 
This  is  clone  repeatedly,  till  nearly  all  the  slag  is  re- 
moved, when  by  a  smaller  and  lighter  skimmer  the  sur- 
face of  the  metal  is  cleaned  entirely  in  the  same  way. 
It  has  often  been  mentioned  that  when  metallic  silver 
is  exposed  in  a  melted  condition  to  the  air,  oxyclation 
takes  place  and  causes  a  loss  by  volatilization.  By  add- 
ing the  borax  with  the  first  charge,  the  silver  will  be 
covered  by  it  and  protected ;  but  when,  by  skimming, 
all  the  slag  has  been  removed,  and  the  metal  surface 
appears  clear,  a  handful  of  charcoal  powder  must  be 
thrown  into  the  crucible  immediately  after  the  last  slag 
has  been  taken  out.  The  crucible  is  then  covered,  and 
the  last  heat  applied. 

If  there  be  matt  present,  it,  being  more  fluid  than  the 
slag,  does  not  adhere  so  well  to  the  skimmer.  After 
the  accumulated  slag  has  been  knocked  off  from  the 
skimmer,  it  is  dipped  as  before,  but  must  be  taken  out 
quicker  and  the  matt  shaken  off  by  a  quick  shake  over 
a  pan  or  water  tub.  This  operation  continues  till  all 
the  matt  is  out.  When  the  metal  appears  clear,  a  small 
piece  of  borax  is  introduced,  and  when  melted  removed 
by  means  of  a  small  skimmer.  Charcoal  dust  is  then 
introduced  and  a  last  good  heat  given.  The  crucible  is 
taken  out  by  a  pair  of  strong  crucible  tongs  (Fig.  15). 


138  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

It  is  placed  before  the  mould,  and  the  contents  poured 
out  in  a  uniform  stream  and  not  too  slow.  The  cast- 
iron  mould  must  be  made  hot,  and  if  required,  smoked 
over  burning  rosin,  so  that  the  whole  inside  appears 
covered  with  soot.  The  mould  must  stand  level.  As 
soon  as  the  metal  is  in  the  mould  it  is  covered  immedi- 
ately with  charcoal  powder. 

In  this  simple  proceeding,  the  look  of  the  bar  depends 
entirely  on  the  greater  or  less  purity  of  the  metal.  It 
will  however  answer  the  purpose,  as  there  is  no  neces- 
sity to  spend  time  and  fuel  in  acquiring  a  nice  bar, 
unless  the  bar  has  to  be  stamped  wTith  the  value,  ready 
for  the  market.  If  not  stamped  by  a  responsible  firm, 
the  bar  must  be  remelted  for  this  purpose,  no  matter 
how  it  looks.  Hence  there  is  no  need  for  the  millman 
to  trouble  himself  in  making  a  nice  bar.  If  a  handsome 
bar  is  desired,  it  must  be  observed  that  after  slagging,  the 
metal  should  appear  with  a  smooth,  mirror-like  surface, 
so  that  objects  may  be  reflected  by  it.  If  not,  if  the 
metal  when  melted  continues  to  evolve  impurities  which 
cloud  the  surface,  a  new  portion  of  borax  must  be  added 
and  stirred  with  a  red-hot  iron,  or  a  red-hot  slip  of  black 
lead  crucible.  Then  the  heat  is  raised  again,  and  the 
operation  may  be  repeated  two  or  three  times,  always 
removing  the  slag  before  adding  borax,  till  the  metal 
appears  lustrous. 

But  in  many  instances,  especially  when  a  great  deal 
of  sulphurets  come  in  the  amalgam,  sulphur  and  other 
impurities  are  so  abundant  that  it  would  take  half  a  day 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  139 

or  more  to  get  rid  of  it  merely  with  borax.  In  such  a 
case,  if  there  are  about  sixty  pounds  of  metal  in  the 
crucible,  after  all  slag  and  matt  have  been  removed,  four 
or  five  ounces  of  lead  are  introduced  with  the  addition  of 
some  borax.  The  metal  is  then  mixed  well,  the  crucible 
covered,  and  the  heat  increased.  When  the  charcoal 
has  burned  down  to  the  brim  of  the  crucible,  the  cover 
is  taken  off,  and  the  slide  doors  of  the  furnace  shut 
partly,  so  that  only  three  to  four  inches  of  opening  is 
left,  otherwise  the  heat  is  oppressive  to  the  workman. 
The  metal  must  be  stirred  over,  and  the  borax  which 
takes  up  the  oxyd  of  lead  and  other  impurities,  separ- 
ated by  the  aid  of  lead,  skimmed  off  and  replaced  by 
another  piece  of  borax.  The  oxyd  of  lead  can  be  seen 
distinctly  in  numerous  little  spots  adjoining  the  borax. 
When  the  last  particles  of  lead  separate  from  the  silver, 
the  surface  of  the  metal  will  brighten  for  a  few  seconds, 
assuming  by  degrees  a  clear  lustrous  appearance.  When 
the  borax  is  saturated  by  the  litharge,  the  crucible  will 
be  attacked.  It  is  therefore  necessary  to  skim  often 
and  to  add  more  borax. 

Such  metal,  also  amalgam  from  roasted  ore,  especially 
if  obtained  in  large  quantities,  is  not  only  cheaper  and 
more  economical  to  refine  in  a  refining  furnace,  like  the 
cupel  furnace  (Sec.  58)  which  should  be  of  a  smaller 
size,  but  even  the  melting  into  bars  is  more  advanta- 
geous and  a  great  deal  less  troublesome  than  the  crucible 
melting,  unless  it  is  very  pure  metal.  Silver,  exposed 
to  the  draft  in  a  melting  condition,  suffers  a  loss  which 


140  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

increases  with  time  and  heat.  For  this  reason  the  melt- 
ing in  crucibles  is  preferable,  if  the  metal  is  pure,  but 
when  oxydation  of  base  metals  is  required,  in  order  to 
refine  the  silver,  a  refining  furnace  must  be  used. 

A  new  test  furnace  ought  to  be  dried  by  a  slow  fire, 
at  least  two  days  before  the  heat  can  be  increased. 
When  the  test  appears  light  red  hot,  a  small  piece  of 
retorted  amalgam  is  introduced  in  the  middle  of  the 
test,  and  the  door  shut.  If  it  melts  into  a  bright  silver 
button  the  amalgam  can  be  charged  as  carefully  as 
possible,  otherwise  the  test  might  be  injured,  especially 
the  first  charge  in  a  new  test.  Several  hanclfuls  of 
charcoal  dust  are  introduced,  the  door  closed,  and  a 
strong  heat  applied.  The  silver  will  soon  commence  to 
melt,  making  room  for  another  charge.  When  the  test 
crucible  is  full,  containing  sixty,  one  hundred,  two  hun- 
dred, or  two  thousand  pounds,  according  to  the  size, 
good  heat  must  be  kept  up  for  about  half  an  hour, 
then  stirred  with  a  red-hot  iron  hook,  the  end  of  which 
is  bent  upwards  so  as  not  to  tear  the  crucible.  The 
charcoal  dust  will  soon  burn  off,  and  must' be  replaced 
by  another  charge  when  the  metal  appears  bright  and 
clear.  It  is  then  ready  to  be  dipped  up  and  poured 
into  moulds  previously  warmed. 

But  if  dry,  ash-like  impurities  appear  on  the  surface 
of  the  metal  bath  some  litharge  may  be  thrown  on  it. 
This  will  fuse,  and  be  drawn  into  the  mass,  taking  the 
impurities  with  it.  The  metal  must  be  stirred  several 
times  and  a  strong  heat  kept  up,  till  after  an  hour  or 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  141 

two,  the  surface  of  the  silver  will  appear  like  a  mirror 
without  agitation.  If,  however,  the  silver  should  con- 
tain a  good  deal  of  foreign  matter,  twenty  or  twenty-five 
ounces  of  lead  may  be  introduced.  The  metal  will  com- 
mence immediately  to  work,  minute  spots  of  litharge 
will  arise  on  the  surface  increasing  and  gliding  towards 
the  test,  by  which  they  will  be  taken  up.  This  will 
continue  for  some  time,  when  the  whole  bath  will  be 
perceived  to  be  covered  suddenly  with  a  bright  cloud 
which  disappears  in  a  few  minutes,  leaving  the  metal 
clear.  As  a  matter  of  course,  no  lead  is  necessary  if 
the  amalgam  is  already  alloyed  with  it,  which  is  easily 
discovered  by  the  blowpipe  (Sec.  2). 

The  hot  mould  is  placed  close  to  the  door,  and  the 
silver  poured  into  it  by  means  of  an  iron  ladle  about 
six  inches  in  diameter  and  two  inches  deep.  This  ladle 
must  be  made  red  hot  before  using.  Near  the  close  of 
the  operation  the  heat  must  be  increased  and  kept  on 
till  all  the  silver  is  out.  A  small  quantity  which  cannot 
be  dipped  out  always  remains.  This  is  left  till  it  cools 
and  becomes  hard,  when  it  is  easily  removed  by  an  iron 
rod.  This,  however,  must  be  done  without  delay  as  soon 
as  the  cake  gets  hard ;  otherwise,  if  too  late,  the  test 
would  certainly  get  damaged.  This  is  of  course  not 
necessary,  if  another  charge  of  silver  has  to  be  melted. 

All  the  slag  and  matt  must  be  carefully  gathered  till 
a  convenient  time  is  found  to  remelt  it.  It  happens 
sometimes  that  the  skimmer  takes  up  a  few  drops  of 
metal  with  the  slag,  especially  if  there  is  not  sufficient 


142  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

heat  in  the  crucible.  The  matt  always  contains  more 
or  less  silver.  The  slag  and  matt,  when  they  are  to  be 
melted,  are  broken  into  small  pieces  by  a  hammer  and 
mixed  with  ten  per  cent,  of  soda-ash  or  soda.  An  old 
crucible  of  a  good  size  (No.  50.)  which  appears  strong 
enough  to  stand  the  melting  is  placed  in  the  furnace  in 
the  same  way  as  for  melting  retorted  amalgam,  and  the 
mixture  is  introduced  by  means  of  a  scoop,  filling  two- 
thirds  of  the  crucible.  It  requires  about  one  hour  to 
melt  one  charge.  When  the  fusion  is  complete,  the 
contents  of  the  crucible  is  stirred  first  with  a  rod  of 
iron  a  quarter  of  an  inch  thick  which  is  bent  over  like 
a  hook.  When  after  some  time,  the  rod  gets  red-hot 
and  the  hook  melts  down,  some  old  nails  or  scrap  iron 
must  be  added  and  stirred  with  a  thicker  iron  rod  from 
time  to  time.  Another  test  is  made  with  the  quarter- 
inch  iron  rod,  and  when  that  rod  no  longer  assumes  a 
white  heat  at  which  it  melts  off,  a  last  strong  heat  is 
applied  and  the  slag  is  removed  by  an  iron  ladle  which 
is  cooled  in  water  after  each  dip.  When  about  two- 
thirds  has  been  removed  in  this  way,  the  crucible  is 
charged  again  and  managed  as  before. 

Silver  matt  when  thus  treated  transfers  its  sulphur  to 
the  iron,  and  the  silver  is  reduced  to  the  metallic  state, 
accumulating  at  the  bottom  of  the  crucible.  So  long  as 
the  test  iron  melts  off  in  a  short  time,  more  iron  must 
be  added.  When,  after  four  or  five  charges  from  which 
the  slag  has  always  been  skimmed  off.  sufficient  metal 
accumulates  in  the  crucible,  it  is  taken  out  and  the  con- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  143 

tents  poured  into  a  warm  mould.  By  adding  lead,  the 
extraction  of  silver  is  more  perfect,  but  then  it  requires 
cupellation  (Sec.  46.) 

The  borax  slag,  especially  when  matt  is  present,  con- 
tains very  little  silver,  except  that  slag  which  involves 
the  matt  in  small  globules.  Therefore  the  shortest  way 
of  beneficiating  slag  and  matt,  is  to  throw  it  on  the  ore 
before  the  battery  and  to  treat  it  in  pans  with  the  ore, 
provided  that  no  roasting  is  in  progress,  because  the 
slag  particles  melt  at  a  very  low  heat,  thus  forming  hard 
little  half-melted  lumps,  which  howTever  are  not  injurious 
if  pan  amalgamation  is  adopted. 

ASSAY  OF  THE  BAR. 

Sec.  44.  It  is  not  the  intention  to  describe  here  the 
way  of  assaying  for  the  purpose  of  stamping  the  value 
on  the  bar,  as  required  for  the  market,  but  merely  to 
ascertain  the  value  for  transportation,  or  to  have  some 
check  on  the  value  to  be  ascertained  in  the  assay  office 
where  it  is  remelted. 

After  the  bar  has  been  cleaned  and  dried,  if  cooled 
in  water,  and  that  is  generally  clone  to  save  time,  two 
little  pieces  are  cut  off  from  the  corners,  one  on  each 
flat  side,  and  the  bar  weighed  on  a  good  platform-scale. 
The  two  pieces  are  flattened  on  an  anvil  thin  enough  to 
be  cut  with  a  pair  of  scissors,  and  heated  to  a  red  heat 
on  a  piece  of  charcoal  with  a  blowpipe. 

As  the  upper  and  lower  sides  of  the  bar  do  not  differ 


144  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

much  in  regard  to  fineness,  provided  that  the  melted 
silver  was  well  mixed  at  the  moment  before  it  was 
poured  into  the  mould,  it  is  sufficient  to  weigh  on  the 
assay  balance  about  five  grains  of  one  piece  and  to  add 
as  much  of  the  other,  so  as  to  weigh  very  exactly  ten 
grains  in  all.  It  is  understood,  of  course,  that  the  silver 
chips  must  be  perfectly  clean.  These  ten  grains  are 
wrapped  in  a  little  piece  of  sheet  lead  of  about  ten 
grains  weight,  or  more  if  copper  is  in  the  metal,  and 
introduced  into  a  cupel  by  a  pair  of  cupel-tongs.  The 
cupel  must  be  light  red-hot  before  the  assay  is  intro- 
duced. It  is  then  cupelled  according  to  the  process 
described  in  Sec.  19,  or  the  cupellation  can  be  performed 
by  the  blowpipe  (Sec.  12).  The  silver  button  is  taken 
from  the  cupel  with  a  pair  of  pincers  and  cleansed  of 
the  adhering  particles  of  bone-ash  with  a  toothbrush.  It 
is  then  hammered  flat  on  an  anvil  and  annealed  again 
with  the  blowpipe  or  in  the  muffle.  It  is  now  weighed 
on  the  balance  and  the  weight  noted.  After  this,  the 
amount  of  gold  must  be  ascertained  by  parting  it  from 
silver.  For  this  purpose,  pure  nitric  acid  (about  three- 
fourths  of  an  ounce)  is  poured  into  a  glass  matrass  or 
tube  and  the  silver  plate  dissolved  as  described  in  Sec. 
19.  The  weight  of  the  gold  is  also  noted,  and  the  calcu- 
lation made  as  illustrated  in  the  following  example : 

For  instance,  the  bar  weighed  on  the  platform  scale 
forty-one  and  one-half  pounds.  This  must  be  multiplied 
by  14-58  to  find  the  amount  of  ounces.  The  silver 
button  after  cupellation  weighed,  say,  887  and  the  gold 
131.    The  value  of  the  bar  will  be  found  thus: 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  145 

The  bar  weighs  41-5  X  14-58  =  605-07  ounces. 
The  fineness  in  silver  is  887-131  =  756  X 1-30  =  value  per  oz.  $0,98-2 
"  "  gold   131  X  20-67      "        «  2,70-7 

Value  of  gold  and  silver  per  ounce  $3,68-9 

Hence  the  value  of  the  bar  is  605-07  X  3-689  =  $2232-10. 

If  the  same  kind  of  ore  is  treated  by  a  permanent 
process,  the  fineness  of  the  silver  varies  generally  very 
little  in  regard  to  base  metals,  except  when  it  comes 
from  the  roasting  process.  It  is  then,  if  not  required  to 
know  the  very  exact  value,  sufficient  to  take  the  aver- 
age fineness  of  some  bars,  say  887,  and  to  make  the 
assay  only  on  gold,  the  amount  of  which  should  be  sub- 
tracted from  887,  leaving  thus  the  silver  for  the  calcula- 
tion very  near  the  real  amount. 

If,  on  account  of  a  high  amount  of  gold,  the  assay 
should  not  dissolve  in  nitric  acid,  pure  silver  must  be 
added.    (Sec.  19.) 


IV.   MELTING  PROCESS. 

Sec.  45.  The  melting  of  silver  ore,  carried  on  in  sev- 
eral metallurgical  works  of  San  Francisco,  other  parts 
of  California,  and  in  Pleasant  Yalley,  N.  T.,  is  compara- 
tively an  expensive  method.  It  is  not  very  likely  that 
silver  ore  ever  will  be  worked  advantageously  by  melt- 
ing, unless  the  amount  of  lead  or  some  particular  cir- 
cumstances should  decide  for  it. 
10 


146  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Very  rich  ore,  which  allows  the  use  of  sufficient 
fluxes,  may  justify  a  proper  melting;  but  even  then, 
amalgamation  in  pans  without  roasting,  with  a  saving 
of  the  tailings  to  be  worked  over  in  pans  or  barrels 
after  a  chlorodizing  roasting,  will  be  preferable  to  the 
expensive  melting,  which  requires  experienced  and 
skillful  hands,  and  a  considerable  investment  of  capital. 

The  reverberatory  furnaces,  which  are  used  in  Cali- 
fornia or  Nevada  Territory,  have  nothing  peculiar  in 
their  construction,  and  resemble,  generally  in  arrange- 
ment, shape,  and  dimensions  those  described  in  metal- 
lurgical books.  These  furnaces  require  the  best  fuel, 
either  imported  coal  or  artificially  dried  wood,  and  do 
not  seem  to  be  suitable  for  the  circumstances  of  Califor- 
nia and  Nevada  Territory.  This,  of  course,  does  not 
allude  to  ore  like  pure  galena,  which  does  not  require 
such  a  heat  as  the  silver  ore,  the  latter  being  generally 
accompanied  by  various  foreign  substances.  However, 
a  description  will  be  given  of  a  crucible  furnace  which 
was  planned  by  the  writer  for  melting  the  rich  Ophir 
ore  in  San  Francisco,  and  which  answered  the  purpose 
perfectly. 

The  blast  furnaces,  where  the  burning  of  coke,  an- 
thracite, or  charcoal,  is  forced  by  compressed  air,  con- 
centrated in  a  small  space,  thus  affording  a  high  tem- 
perature, even  if  a  lower  quality  of  fuel  must  be  used, 
are  more  suitable,  under  our  circumstances,  for  melting 
silver  ore,  provided  that  sufficient  lead  ore,  containing 
at  least  fifty  per  cent,  of  lead,  can  be  mixed  with  it. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  147 

This  kind  of  furnace  is  also  more  easily  constructed, 
not  absolutely  requiring  fire  brick,  for  which  some  kinds 
of  sand  stone,  conglomerate  with  predominant  quartz, 
or  some  clay  slate  may  be  substituted.  The  disadvan- 
tage is  the  want  of  power  to  drive  the  bellows,  which 
is  the  soul  of  the  furnace.  The  shape  and  dimensions 
are  described  in  all  metallurgical  books.  Besides^  the 
dimensions  and  the  whole  arrangement  should  be  accom- 
modated to  the  locality  and  the  ore. 

The  crucible  furnace  (Sec.  57,  Figs.  32,  33,  34),  de- 
rived from  the  Mexican  cupel  furnace,  can  melt,  accord- 
ing to  the  size  and  quality  of  ore  and  fuel,  from  half  a 
ton  to  three  tons  in  twenty-four  hours.  The  ore  is  pul- 
verized and  sifted  in  a  sieve  of  about  six  hundred  and 
twenty-five  holes  to  the  square  inch.  The  ore  can  be 
melted  directly,  when  mixed  with  fluxes ;  but  it  is  more 
economical  to  roast  it  after  it  has  been  pulverized,  in 
order  to  drive  out  as  much  sulphur  as  is  possible,  at  a 
low  heat.  If  subjected  to  melting  without  roasting,  a 
great  deal  of  metallic  iron  is  required  to  consume  all 
the  sulphur. 

Iron,  lead,  silver,  and  copper,  combine  with  the  sul- 
phur and  form  a  matt  which  covers  the  lead  below  the 
slag.  This  matt  must  be  roasted  and  treated  like  ore. 
It  will  also  be  formed,  to  some  extent,  even  after  a  good 
roasting,  and  it  would  not  be  advisable  to  roast  so  per- 
fectly as  to  prevent  the  formation  of  matt,  because  the 
slag  will  always  be  poorer  in  silver,  if  some  matt  is 
made  in  melting. 


148  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

The  roasting  is  performed  in  a  common  roasting  fur- 
nace, at  a  very  low  heat,  with  diligent  stirring,  continu- 
ing till  no  sulphurous  gas  is  emitted,  which  can  be 
ascertained  by  the  odor.  This  operation  may  require 
three  hours.  To  each  new  charge  of  ore  some  pulver- 
ized matt  should  be  added,  so  that  it  shall  not  accumu- 
late.   It  may  be  pulverized  with  the  ore,  or  separately. 

The  roasted  ore  is  then  mixed  with  fluxes,  of  which 
there  are  three  classes : 

1.  Fluxes,  dissolving  the  different  earths  and  oxyds  of 
base  metals.  Such  fluxes  are  :  soda  ash,  litharge,  slag, 
and  silicia  or  quartz. 

2.  Fluxes,  decomposing  sulphurets  :  metallic  iron,  lith- 
arge, and  lime  ;  also,  soda  ash. 

3.  Fluxes,  collecting  the  gold  and  silver :  lead,  in  the 
the  shape  of  granulated  metallic  lead,  or  as  lead  ore ; 
litharge,  or  hearth  (the  mass  from  the  refining  furnace). 

The  litharge,  or  lead-oxyd,  which  is  obtained  from  the 
cupel  furnace,  consisting  of  92*8  lead  and  7*17  oxygen, 
eagerly  dissolves  the  quartz  and  other  earths  forming 
silicates.  It  is  also  a  powerful  agent  in  decomposing 
sulphurets  by  its  oxygen,  creating  sulphurous  acid  and 
metallic  lead,  which  latter  combines  with  the  metal  of 
the  sulphuret  and  all  metallic  particles  with  which  it 
may  come  in  contact. 

The  addition  of  slag  in  melting  has  a  double  purpose : 
first,  to  dissolve  the  earths  and  oxyds  of  metals  •  second, 
to  regain  the  particles  of  lead  and  matt  which  were 
drawn  out  with  the  slag,  in  cleaning  the  surface  of  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  149 

lead  before  tapping.  If  there  be  not  a  sufficiency  of 
such  slag,  poorer  slag  must  be  added. 

The  silicia,  in  the  shape  of  sand,  dissolves  the  oxyd 
of  iron.  The  addition  of  sand  is  required  when  roasted 
matt  is  melted  without  sufficient  ore  to  mix  with  it.  In 
this  case,  if  no  sand  were  used,  the  oxyds  of  iron  and 
lead  would  attack  the  mass  of  the  hearth  considerablv. 

The  lime  combining  with  the  slag,  protects  the  oxyd 
of  lead  against  such  combination  and  decomposes  the 
sulphurets  indirectly. 

The  hearth  of  the  cupel  is  used  on  account  of  being 
saturated  with  litharge. 

The  charcoal  in  the  pulverized  state  decomposes  the 
oxyd  of  lead  and  in  part  the  sulphates.  It  is  used  in 
such  proportion  as  to  reduce  one  part  of  the  litharge, 
while  another  part  decomposes  the  sulphurets  which 
may  remain  in  the  ore  after  roasting. 

Metallic  iron  (granulated  or  borings)  is  the  best  agent 
for  the  decomposition  of  sulphurets  forming  iron  matt. 

Metallic  lead  takes  up  the  gold  and  silver  whenever 
it  comes  in  contact  with  these  metals  or  melted  sul-» 
phurets.  No  melting  of  silver  ores  can  be  performed 
without  lead  or  materials  which  produce  lead.  If  there 
is  no  lead  ore,  granulated  lead  or  litharge  will  answer 
even  better  (but  not  in  a  blast  furnace).  Litharge  must 
be  pulverized  and  sifted.  -  The  lead  requires  to  be  finely 
granulated.  The  granulation  is  effected  in  a  wooden 
box  (Fig.  19).  The  bottom  and  sides  must  be  smooth, 
and  the  box  tight.    The  box  hangs  on  a  rope  so  as  to 


150  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

allow  a  swinging  motion.  Several  hundred  pounds  of 
lead  are  melted  in  an  iron  kettle  and  kept  in  a  fused 
condition  by  a  slight  fire  underneath.  The  temperature 
of  the  lead  is  right  when  a  wooden  stick  thrust  into 
it  turns  brown  without  causing  a  boiling  motion.  About 
twenty  pounds  are  then  taken  with  a  hot  crucible  or 
an  iron  ladle  and  introduced  into  the  box,  in  which  a 
handful  of  pulverized  charcoal  was  previously  put.  This 
must  be  repeated  at  each  charge. 

The  workman  immediately  takes  hold  of  the  handles, 
a,  and  swings  the  box  in  such  a  way  that  the  lead 
slides  from  the  side,  b,  over  to  cy  and  back,  and  so  on 
repeatedly.  When  the  lead  becomes  more  compact  by 
cooling,  the  swinging  must  be  shorter  and  quicker,  so 
that  the  lead  strikes  the  sides  with  force  till  it  falls  in 
dust.  The  box  is  turned  over  and  another  charge  gran- 
ulated. The  lead  thus  granulated  must  be  sifted  in  a 
sieve  of  about  six  hundred  and  twenty-five  holes  to  the 
square  inch. 

Lead  ore  is  preferable  to  lead  or  litharge  only  in  case 
4hat  it  contains  some  silver,  or  if  it  is  cheaper.  The  ore 
must  be  selected  carefully  and  all  rubbish  separated. 
It  should  contain  seventy  or  seventy-five  per  cent,  of 
lead,  never  less  than  fifty.  If  the  ore  is  galena  (sul- 
phuret  of  lead)  it  should  be  mixed  with  the  ore  in 
the  right  proportion  before  pulverization  and  roasted 
together  with  an  addition  of  matt,  obtained  in  course 
of  melting.    The  proportion  of  ore  and  fluxes  may  be 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  151 

changed  according  to  the  nature  of  the  ore ;  the  follow- 
ing mixtures,  however,  may  be  given : 

No.  1.    Mixture  for  Ores  without  Roasting  and  before 
Litharge  is  obtained  from  the  Manipulation. 


Silver  ore  100  pounds. 

Granulated  lead  (or  200  pounds  lead  ore)   85  pounds. 

Soda  ash   25  pounds. 

Iron   25  pounds. 

Lime  (and  25  pounds  slag  when  obtained)   3  pounds. 

No.  2.    Mixture  for  Roasted  Ore. 

Silver  ore  100  pounds. 

Granulated  lead   85  pounds. 

Soda  ash   20  pounds. 

Iron   8  pounds. 

Lime   3  pounds. 

No.  3.   Mixture  of  Silver  Ore  after  Products  of  Smelting 
are  at  Hand. 

Silver  ore  100  pounds. 

Granulated  lead   25  pounds. 

Litharge   75  pounds. 

Hearth   10  pounds. 

Soda  ash   15  pounds. 

Charcoal   5  pounds. 

Iron   8  pounds. 

Lime   3  pounds. 

Slag   25  pounds. 


When  the  melting  is  executed  with  an  addition  of 
lead  ore,  No.  2.  and  No.  3  do  not  require  granulated 


152  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

lead,  but  it  is  always  very  useful  to  add  sufficient 
litharge.  The  quantity  of  flux  required  depends  much 
on  the  quality  of  ore.  If  the  slag  is  too  thin,  it  is  not 
necessary  to  use  so  much  soda  ash. 

When  the  furnace  is  white-hot,  the  mixture  is  intro- 
duced by  means  of  a  scoop  or  shovel  at  the  flue  door 
(Fig.  32,  i),  and  spread  to  about  half  the  length  of  the 
flue,  between  the  door  and  the  crucible.  The  ore  may 
lie  five  or  six  inches  deep.  The  door  is  closed,  and  the 
firing  continued  so  that  the  flame  reaches  the  end  of 
the  flue.  The  ore  soon  commences  to  melt,  and  runs 
into  the  crucible.  A  new  charge  must  be  introduced  as 
often  as  the  melting  ore  makes  room  for  it.  On  the 
melting  surface  of  the  ore  innumerable  lead  globules 
arise,  which,  taking  up  silver,  grow  bigger  by  joining 
other  globules,  and  roll  down  into  the  crucible,  followed 
by  the  slag.  The  lead  separates  in  the  crucible  from 
the  slag  and  matt,  and  it  is  very  important  to  open  the 
front  door,  k,  often,  in  order  to  mix  the  slag  and  lead 
well  by  stirring  with  an  iron  rod,  which  is  bent  hook- 
like in  such  a  way  that  the  crucible  may  not  be  injured. 
The  more  the  lead  is  brought  into  contact  with  slag,  the 
poorer  the  latter  will  be  in  silver.  The  melting  goes  on 
till  the  crucible  is  nearly  full ;  but  care  must  be  taken 
to  stop  charging  in  time,  so  that,  when  the  crucible  is 
full,  no  ore  shall  be  in  the  flue.  The  melted  mass  is 
now  stirred  again,  the  door  closed,  and  a  good  heat 
applied  for  fifteen  minutes,  after  which  the  .firing  is 
stopped  and  the  slag  channel  opened  by  means  of  a  bar. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  153 

The  slag  runs  out  in  an  iron  car.  The  channel  is  then 
shut  again  by  a  paste,  formed  of  one  part  of  ashes  in 
bulk,  and  one  of  loam,  well  mixed.  The  paste  must  be 
made  soft,  but  still  so  that  it  may  be  formed  into  round, 
long  pieces,  which,  after  being  dipped  in  water,  are  laid 
directly  into  the  hot  channel  and  pressed  with  a  piece 
of  red-hot  flat  iron.  This  operation  must  be  repeated 
after  each  introduction  of  the  paste  till  the  channel  is 
filled  level  with  the  rim  of  the  crucible. 

The  fire  is  started  again,  the  flue  charged  with  ore, 
and  the  melting  executed  in  the  same  way  as  before. 
After  the  slag  has  been  discharged  five  or  six  times,  it 
may  be  examined  by  an  iron  ladle,  to  ascertain  how 
much  lead  or  matt  has  accumulated  in  the  crucible,  and 
when  it  is  found  that  the  matt  is  only  three  inches  be- 
low the  bottom  of  the  slag  channel,  the  slag  is  first  dis- 
charged into  the  car,  and  when  it  has  run  out,  the  re- 
mainder must  be  drawn  off  by  an  iron  hoe  through  the 
channel  till  the  matt  appears  free  from  slag.  The  slag 
thus  drawn  off  is  mixed  with  the  ore  again,  as  men- 
tioned before,  for  some  matt  will  unavoidably  be  drawn 
out  likewise.  When  all  the  slag  has  been  removed  from 
the  crucible,  the  lead  and  matt  must  be  tapped  into  the 
open  hearth,  B\  The  taphole  is  opened  with  a  chisel- 
like pointed  bar,  boring  and  picking  the  loam  mixture 
in  the  hole,  not  using  too  much  force,  till  the  lead  com- 
mences to  run  out. 

When  all  is  out,  the  taphole  must  be  closed  again 
without  delay.    For  this  purpose  a  piece  of  charcoal, 

k 


154  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

about  two  and  a  half  inches  long,  pointed  at  one  end 
wrapped  with  loam  at  the  other,  and  shaped  like  the 
taphole,  is  fastened  to  a  rod,  and  introduced  so  that  the 
point  of  the  charcoal  shuts  up  the  hole  in  the  crucible. 
Two  or  three  other  loam  balls  are  applied  on  it,  tapping 
each  with  a  wooden  rod. 

The  matt,  separated  from  the  lead,  hardens  quicker 
than  the  lead  below  it  in  the  lower  hearth,  and  can  be 
removed  in  one  piece  with  an  iron  fork.  The  lead  is 
then  dipped  up  with  ladles  and  poured  into  warm  iron 
moulds.  The  lead  bars  weigh  twenty-five  or  thirty 
pounds,  a  convenient  size  for  handling  at  the  cupel  fur- 
nace. 

All  the  matt  is  turned  into  the  ore  and  pulverized 
with  it.  In  roasting,  the  sulphur  is  burnt  off  and  the 
iron  oxydized,  being  thus  a  good  flux  for  the  silicia, 
while  the  silver  is  absorbed  by  the  lead. 

SEPARATION  OF  LEAD  AND  SILVER,  OR  CUPELLA- 

TION. 

Sec  46.  The  lead,  obtained  from  melting  silver  ores, 
must  be  separated  from  the  silver  by  an  oxydizing  pro- 
cess, called  cupellation.  To  this  the  lead  is  subjected 
either  directly,  or,  if  very  poor  in  silver,  after  concen- 
tration in  a  smaller  quantity  of  lead,  in  order  to  reduce 
the  expense  of  cupellation.  This  (Pattinson's)  concen- 
tration has  been  introduced  by  Capt.  Mead  in  Pleasant 
Valley,  N.  T.,  the  result  of  which  is  not  yet  known. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  155 

Some  general  remarks  on  the  concentration  by  crystal- 
lization will  follow,  after  the  cupellation  shall  have  been 
described. 

The  cupel  furnace  (Sec.  58,  Figs.  35,  36),  after  having 
been  perfectly  dried  by  a  slow  fire  for  two  or  three  days, 
must  be  made  light  red-hot,  before  the  lead  can  be  intro- 
duced. A  piece  of  lead  is  placed  on  the  hearth,  and 
observed.  First  it  will  melt  and  become  covered  with 
an  oxyd.  If  the  heat  is  too  low,  the  oxyd  coat  grows 
thicker,  and  the  lead  remains  dark  red.  In  this  case  the 
door  is  shut  and  the  temperature  raised  by  better  firing. 
The  oxyd  crust  will  then  melt  and  disappear,  leaving  a 
round,  bright  lead  button.  When  this  is  perceived,  two 
lead  bars  are  introduced,  placed  on  the  fire-tile,  and  re- 
placed by  others  when  melted  down,  till  the  hearth  is 
full.  If  the  lead  is  not  clean,  there  remains  on  the  tile 
a  kind  of  skeleton,  mostly  of  matt,  which  is  pushed  into 
the  test  before  another  lead  bar  is  introduced.  The 
doors  are  closed,  and  the  heat  raised.  After  half  an 
hour's  time  the  surface  of  the  leadbath  is  covered  with 
a  kind  of  slag,  the  scrapings,  consisting  of  oxyds  of  lead 
and  iron,  and  other  foreign  matters.  These  scrapings,  to 
be  melted,  require  more  heat  than  the  litharge,  and  are 
called  froth.  This  froth  is  drawn  off,  over  the  litharge 
bridge  (Fig.  36,  /),  in  which  a  small  canal,  e\  is  made 
just  before  drawing.  For  this  purpose  a  piece  of  flat 
iron  is  prepared,  about  one  and  a  half  inches  wide  by 
one-half  inch  thick  and  five  feet  long,  one  end  of  which 
is  sharpened  and  stretched  a  little,  so  that  it  assumes 


156  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

the  shape  of  a  chisel.  With  this  instrument  the  canal  is 
made  by  careful  picking  and  scratching,  about  half  an 
inch  deep. 

Over  this  canal  the  scrapings  must  flow  from  the 
furnace.  To  effect  this,  the  slag  is  drawn  first  with  a 
round  iron  rod  over  the  channel  repeatedly,  holding  the 
rod  light  on  the  surface  of  the  bath,  or  otherwise  some 
lead  might  escape.  The  scrapings,  assisted  in  this  way, 
will  soon  flow  by  themselves,  but  from  time  to  time 
they  require  again  the  aid  of  the  rod.  The  easy  run 
depends  also  on  the  temperature  ;  if  too  low,  the  scrap- 
ings will  freeze  and  shut  up  the  canal.  This  slag  looks 
black,  is  heavy  and  brittle  and  shows  a  glassy  surface. 
By  degrees  it  changes  color,  becoming  more  yellow, 
flowing  more  easily,  and  assuming  a  scaly  appearance. 
The  litharge  is  formed  now,  and  flows  freely  through 
the  canal,  which  however  must  be  constantly  attended 
to  by  widening  in  case  of  need,  or,  by  arresting  the 
stream  by  putting  a  small  lump  of  the  hearth  mass  in 
the  canal,  if  any  drops  of  lead  escape.  The  heat  must 
be  kept  moderate  and  regulated  after  the  appearance  of 
the  litharge.  As  long  as  the  scrapings  continue  to  run, 
the  temperature  requires  to  be  higher  so  that  the  scrap- 
ings flow  down  to  the  floor.  When  so  much  of  this 
slag  is  removed  that  the  lead  is  exposed  in  the  middle 
of  the  bath,  the  blast  is  introduced,  first  gently  blowing, 
but  it  may  be  increased  when  litharge  arises  to  such  a 
degree  that  the  lead  is  slightly  moved  by  the  wind  and 
the  litharge  is  driven  against  the  sides.    The  lead  bath 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  157 

brightens  and  must  be  always  lighter  in  color  than  the 
hearth  at  the  sides.  When  the  litharge  solidifies  on  the 
bridge  or  shortly  below  it,  the  operation  requires  more 
heat.  The  right  temperature  is  then  when  the  litharge 
flows  to  the  floor,  but  when  it  flows  on  the  floor  in  a  red- 
hot  condition,  there  is  too  much  heat  in  the  oven,  caus- 
ing a  greater  loss  in  lead  by  volatilization. 

When  the  litharge  ceases  to  flow  at  the  right  temper- 
ature, the  canal  must  not  be  made  deeper,  but  another 
lead  bar  placed  on  the  tile.  It  requires  much  attention 
to  keep  the  canal  as  uniform  as  possible  about  half  an 
inch  wide.  This  canal  will  be  cut  deeper  gradually 
by  the  litharge.  If  the  temperature  is  too  high  the  lith- 
arge attacks  the  hearth-mass  more,  the  canal  will  grow 
deeper  and  some  lead  may  escape.  When,  therefore, 
after  a  longer  use,  or  with  excessive  heat,  the  canal 
appears  too  deep,  it  must  be  filled  with  hearth-mass  and 
another  canal  opened  alongside  of  it  as  flat  as  possible, 
just  to  permit  the  flowing  of  the  litharge.  The  charging 
of  lead  bars  must  continue  without  interruption,  regu- 
lated by  the  canal  and  the  formation  of  litharge  as 
above  described. 

In  drawing  the  litharge,  it  is  an  error  to  let  all  flow 
out.  Particular  attention  must  be  paid  to  have  at  least 
fojir  or  five  or  even  more  inches  of  the  surface  of  the 
lead  always  covered  with  litharge,  which  forms  a  flat 
ring  on  the  periphery  of  the  bath.  The  longer  the 
litharge  is  in  contact  with  the  lead  the  poorer  it  is  in 
silver.    Another  sign  for  the  right  temperature  is  in 


158  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  lead  fumes.  If  the  heat  is  too  strong,  the  lead  fume 
will  arise  in  such  a  quantity  that  it  is  difficult  to  see  the 
bath,  which  interferes  very  much  with  the  drawing  o 
the  litharge.  If  on  the  other  hand  the  temperature  is 
too  low,  the  lead  vapors  will  disappear  almost  entirely, 
the  litharge  does  not  flow  right,  cools  in  the  channel  and 
stops.  The  right  temperature  is  indicated  by  a  moder- 
ate amount  of  lead  vapors,  so  that  most  of  the  litharge 
can  be  seen  distinctly  and  the  flow  is  free,  over  the 
whole  litharge  bridge. 

When  after  twelve  or  fifteen  hours  the  whole  surface 
of  the  bridge  has  been  cut  for  canals,  generally  five  or 
six  of  them,  the  first  one  must  be  opened  again  or  better 
a  new  one  made,  but  of  course  deeper  than  the  first  row. 
The  lead  bath  will  stand  accordingly  also  deeper  in  the 
test.  We  now  proceed  in  the  same  way,  making  new 
canals  close  by,  when  the  first  is  getting  too  deep  and 
so  on.  After  from  thirty  to  forty-eight  hours  of  uninter- 
rupted cupellation,  the  charging  of  lead  bars  is  stopped. 
From  this  moment  the  last  canal  must  be  made  deeper 
as  the  drawing  of  the  litharge  requires  it. 

During  the  whole  process  the  formation  of  litharge 
can  be  observed,  and  it  flows  constantly  on  the  convex 
surface  of  the  bath  towards  the  sides  joining  the  ring 
of  litharge,  kept  purposely  to  some  extent,  in  large 
furnaces  even  twelve  inches  wide.  At  the  end  of  the 
operation  when  the  silver  is  concentrated  and  but  little 
lead  in  it,  the  litharge  appears  less,  but  in  larger  spots, 
till  at  last  a  shining,  playing  veil  appears,  which  soon 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  159 

j  covers  all  the  metal.  The  blast  must  be  moderated  now 
and  the  heat  increased.  After  some  time  the  bath 
clears  up  again,  emitting  some  litharge  in  minute  parti- 

j  cles  which  continue  under  strong  heat  for  a  short  time. 
The  blast  must  be  reduced  now  to  the  lowest  degree 
and  then  stopped  entirely,  when  the  silver  commences  to 
play  rainbow  colors,  but  the  fire  must  be  kept  on.  The 
silver  is  stirred  with  a  red-hot  iron  rod  once  or  twice 
till  finally  the  metal  appears  bright  and  clear  like  a 
mirror.  If  there  are  eighty  pounds  or  more  of  metal 
in  the  test,  the  silver  may  be  dipped  out  with  an  iron 
ladle  into  hot  moulds.  Smaller  quantities  are  cooled  by 
the  blast,  also  some  cold  water  may  be  poured  on  the 
middle  of  the  silver  cake,  yet  only  a  little  at  a  time,  so 
as  not  to  cool  the  hearth  too  much.  When  the  silver 
hardens,  it  emits  oxygen,  forming  figures  or  towers  of 
different  shape.  The  silver  is  then  tried  with  an  iron 
bar,  slightly  knocking  on  it.  If  it  sounds  like  solid 
metal,  a  pointed  bar  will  lift  the  cake  by  introducing 
the  point  under  the  edge  of  the  slab.  The  moment 
when  the  silver  becomes  hard,  must  be  watched  in  this 
operation,  else,  if  too  late,  the  test  might  be  considerably 
damaged.  In  case  the  cake  is  larger  than  the  opening 
of  the  litharge  bridge,  it  must  be  taken  out  through  the 
fire-place. 

The  cupellation,  executed  in  the  described  way,  yields 
very  fine  silver,  which  need  not  be  refined.  Generally 
the  cupellation  is  interrupted  when  the  brightening 


160  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

occurs.  Iii  this  case,  however,  the  silver  is  not  quite 
pure  and  must  be  refined  in  a  refining  furnace. 

As  soon  as  the  silver  is  taken  out,  the  furnace  must 
be  immediately  prepared  for  another  operation,  if  suffi- 
cient pig  lead  is  at  hand.  For  this  purpose,  three  or 
four  flat  iron  bars,  each  five  feet  long,  are  introduced  into 
the  furnace,  so  that  one  end  of  each  may  get  red-hot, 
while  the  other  ends  remain  cold  enough  to  be  handled. 
Meanwhile  the  same  composition,  of  which  the  hearth 
was  made  (Sec.  58),  is  prepared  with  some  water  to  a 
soft  paste,  well  worked,  and  formed  into  cylinder-like 
pieces,  about  eight  inches  long  and  three  or  four  inches 
thick,  of  which  from  four  to  six  pieces  may  be  required. 

The  canal  is  cleaned  of  litharge,  and  one  of  the  pre- 
pared oblong  pieces  dipped  into  water,  and  by  means  of 
a  flat,  cold  iron,  placed  in*the  hot  canal.  The  mass  in- 
troduced must  be  pressed  and  slightly  beaten  with  one 
of  the  red-hot  bars  till  it  seems  to  be  well  united.  This 
operation  must  be  performed  quickly,  so  that  the  oblong 
mass  is  quite  wet  when  touching  the  canal,  and  is  then 
instantly  pressed  and  beaten.  Another  slab  follows  now 
exactly  in  the  same  way,  and  so  on,  until  the  canal  is 
filled  level  with  the  hearth,  forming  a  solid  mass.  When 
this  is  done,  fuel  is  introduced  into  the  furnace  quite 
moderately  for  half  an  hour,  in  order  to  dry  the  new 
litharge  bridge.  The  heat  is  then  increased,  and  when 
the  furnace  appears  light  red-hot,  the  charging  and 
cupelling  of  the  lead  is  performed  in  the  way  described. 

This  operation  can  continue  for  one  or  two  weeks, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  161 

according  to  the  quality  of  the  hearth.  If,  however,  it 
were  required  to  suspend  the  operation  for  one  or  more 
days,  the  hearth  would  crack  in  cooling,  if  not  provided 
for.  In  this  case,  after  the  new  litharge  bridge  has  been 
made,  the  hearth  and  bridges  are  covered  with  ashes, 
and  all  draft  shut  as  off  close  as  possible. 

In  mending  the  canal,  much  attention  must  be  paid 
to  the  right  consistency  of  the  mass,  and  to  having  it 
wet  immediately  before  the  application.  The  mass 
must  be  soft,  but  must  retain  the  form  given  to  it.  If 
too  hard,  or  if  the  dipping  into  water  be  neglected,  the 
lead  would  find  its  way  through,  coming  forth  in  drops. 
In  such  cases  where  the  drops  are  perceived,  the  hearth 
is  hollowed  about  three  inches  deep,  and  stopped  with 
some  of  the  mass,  using  a  red-hot  iron. 

The  litharge,  if  required,  can  be  easily  reduced  to 
metallic  lead  by  having  a  cylinder  of  cast  iron  in  front 
of  the  litharge  bridge.  The  cylinder  is  hollow,  open  at 
both  ends,  and  the  sides  have  a  number  of  inch  holes  to 
admit  the  air.  It  stands  over  a  cast-iron  bowl,  or  on  the 
floor,  in  which  a  hole  is  made  for  the  reception  of  lead. 
The  cylinder  is  filled  with  charcoal  and  set  on  fire,  being 
about  four  feet  high  and  twelve  inches  in  diameter.  The 
litharge  is  led  over  an  iron  plate  into  the  centre  of  the 
cylinder.  The  oxyd  of  lead,  fused  and  red-hot,  coming 
into  contact  with  glowing  coals,  is  reduced  to  lead,  and 
accumulates  in  the  crucible  below  the  cylinder,  which 
must  always  be  kept  filled  with  charcoal. 
11 


162  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


REFINING  OF  SILVER. 

Sec.  47.  The  refining  of  silver  is  the  continuation  of 
cupellation,  when,  as  before  described,  the  process  is 
considered  finished  with  the  brightening  of  the  silver. 
To  this  process  all  impure  silver  is  subjected,  but  when 
copper  or  impurities  are  considerable,  so  that  a  pro- 
portionate quantity  of  lead  must  be  added,  requiring 
also  a  blast  to  effect  the  oxydation,  and  a  litharge  canal 
to  draw  off  the  litharge,  then  the  refining  is  performed 
by  way  of  cupellation.  Retorted  amalgam,  obtained  by 
the  pan  amalgamation  without  roasting,  when  melted 
into  bars,  is  generally  between  987  and  997  fine,  not 
requiring  any  further  refining.  But  in  some  cases  the 
amalgam  contains  sulphurets,  the  sulphur  of  which  re- 
mains to  a  considerable  amount  in  the  silver,  when 
melted  in  the  crucible.  In  pouring  the  metal  into  the 
mould,  sulphurous  acid  is  emitted,  and  its  evolution  con- 
tinues till  the  metal  hardens,  causing  a  dull,  uneven  sur- 
face. Such  amalgam,  as  well  as  that  from  roasted  ore, 
or  silver,  generally,  if  obtained  in  large  quantities,  can 
be  melted  to  advantage  in  refining  furnaces. 

The  refining  is  performed  in  different  ways.  It  is 
done  in  crucibles,  having  thus  the  smallest  loss  in  sil- 
ver ;  but  only  such  silver  as  contains  a  small  amount  of 
impurities  can  be  treated  for  this  purpose  in  crucibles, 
which,  on  the  other  hand,  besides  requiring  more  fuel, 
are  more  dangerous  than  the  hearths,  on  account  of 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  163 

being  liable  to  break,  and  also  expensive.  The  refin- 
ing is  also  executed  in  cast-iron  dishes,  which  are  lined 
with  fire-proof  material.  These  tests  are  placed  in  the 
refining  furnace,  exposed  to  the  flame,  or  under  a  muffle, 
the  last  method  requiring  more  fuel  and  silver  not  too 
impure. 

The  most  proper  way  is  to  refine  in  hearth  furnaces. 
(Sec.  59.)  There  is  little  difference  between  them  and 
the  cupelling  furnaces  in  regard  to  size,  and  no  blast  is 
used  in  either.  The  consumption  of  fuel  is  moderate, 
and  also  the  loss  of  silver,  if  properly  attended  to.  The 
quantity  of  silver  which  can  be  refined  at  a  time  varies, 
according  to  the  size  of  the  furnace,  from  one  hundred 
to  two  thousand  pounds.  These  furnaces  may  be  con- 
structed to  be  heated  either  by  flame  or  gas.  The  gas 
is  produced  by  charcoal,  coke,  or  anthracite. 

The  silver  is  introduced  when  the  test  appears  white- 
hot.  The  door  is  closed  and  the  fire  kept  up  till  all  the 
silver  is  melted.  The  retorted  amalgam,  on  account  oi 
its  bulk,  can  be  charged  at  once.  Another  portion  is 
introduced  and  so  on,  till  the  test  is  full.  When  the  last 
charge  is  melted,  the  silver  must  be  stirred  with  an  iron 
rod  for  a  short  time,  and  then  the  door  is  closed  again 
for  half  an  hour.  If  there  are  still  ash-like  impurities, 
swimming  on  the  surface,  they  may  be  skimmed  off, 
or  one  per  cent,  of  lead  is  introduced  into  the  silver 
and  stirred  again.  The  litharge  will  appear  soon  on  the 
surface  and,  dissolving  the  dry  scrapings,  draw  into  the 
test.    The  stirring,  at  interval  of  half  an  hour  maj  be 


164  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

repeated  three  or  four  times  during  the  process.  The 
silver  becomes  gradually  clearer  and  brighter  till  finally 
the  roof  of  the  furnace  is  reflected  on  the  lustrous  sur- 
face of  the  bath.  At  this  point  the  silver  possesses  the 
required  fineness  of  about  999*5,  and  to  prevent  its 
volatilization  its  surface  must  be  covered  with  charcoal 
powder  immediately.  The  metal  may  be  dipped  up  and 
poured  into  moulds,  keeping  up  continually  a  strong 
heat,  or  it  may  be  cooled  in  the  furnace  and  taken  out 
in  the  shape  of  a  cake,  in  the  same  way  as  described  in 
Sec.  46.  The  melting  may  require  two  or  three  hours 
and  about  the  same  time  must  be  spent  for  refining, 
so  that  the  whole  process  takes  from  five  to  eight  hours, 
according  to  the  quantity  of  silver  introduced. 

PATTTNSON'S  CRYSTALLIZATION  PROCESS. 

Sec.  48.  This  process,  for  the  purpose  of  concentrat- 
ing the  silver  in  the  lead,  is  founded  on  the  fact  that' 
lead,  if  alloyed  with  silver  to  a  certain  proportion,  is 
more  liquid  than  pure  lead,  or  lead  alloyed  in  a  very 
small  proportion  with  silver.  The  advantage  of  this 
process  is  the  reduction  of  the  quantity  of  lead,  which 
otherwise  would  have  to  be  separated  from  silver  by 
cupellation. 

When  a  sufficient  quantity  of  lead,  containing  silver, 
is  melted  in  a  cast-iron  vessel  and  uniformly  cooled,  small 
crystals  will  form,  increasing  in  quantity.  These  crys- 
tals, when  taken  out  by  means  of  perforated  ladles,  will 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  165 


be  found  a  great  deal  poorer  in  silver  than  the  fluid 
remainder  in  the  kettle,  which  again  will  be  found 
richer  than  the  original  lead. 

On  account  of  the  adherence  of  fluid  lead  to  the  crys- 
tallized, the  separation  cannot  be  perfect,  but  repeated 
recrystallization  of  the  crystals  results  finally  in  two 
sorts  of  very  poor  and  rich  lead.  There  is,  however,  a 
limit,  beyond  which  no  concentration  to  a  higher  degree 
can  be  effected. 

According  to  Professor  Reich,  the  melting  tempera- 
ture of  lead,  containing  0*0065  per  cent,  of  silver  is  610° 
Fahrenheit.  Lead,  containing  0*476  per  cent,  of  silver 
melts  at  588°;  but  lead  containing  2*25  per  cent,  of 
silver  melts  at  the  same  temperature  as  pure  lead,  con- 
sequently no  crystallization  of  poor  lead  can  take  place. 
Alloys  of  equal  parts  of  both  metals,  or  three  parts  of 
lead  to  one  of  silver,  require  a  higher  temperature  of 
melting  than  pure  lead. 

The  following  table  shows  the  proportionate  progress 
of  the  enrichment  of  lead,  by  crystallization  of  the  poor : 


Amount  of  silver  in 
pig  lead. 


Amount  of  silver  clipped 
in  crystals. 


Amount  of  silver  in  the 
liquid  remainder. 


0*704  per  cent 

0-732  " 

0-966  « 

0-  988  " 

1-  442  « 

2-  090  « 
2-206  " 
2-206  " 


0-390  to  0-466. 
0.318  "  0-374. 
0-410  "  0-680. 
0-390  «  0-624. 

0-682  

2011  

2-216  

2-212  


1-025 
1-076 
,1-450 
1-530 

1-  922 

2-  260 
2-246 
2-264 


166  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

The  good  result  of  this  manipulation  depends — 
L  On  the  right  management  of  the  temperature, 
the  temperature  be  too  low,  no  separation  can  be  obtain- 
ed, and  if  on  the  other  hand  the  lead  is  too  hot  no  per- 
fect formation  of  crystals  can  take  place. 

2.  On  the  right  quantity  of  lead  which  is  taken  into 
operation.  It  requires  at  least  two  tons  and  a  half,  in 
order  to  effect  a  slow  change  from  the  fluid  into  solid 
condition,  affording  thus  sufficient  time  to  remove  the 
crystallized  lead. 

3.  On  the  number  and  size  of  iron  kettles,  depending 
on  the  quantity  of  lead  designed  for  this  process  and  on 
the  amount  of  silver  in  it. 

The  right  temperature,  the  time  of  crystallization, 
and  the  preservation  of  temperature  must  be  found  by 
experiments.  The  use  and  advantage  of  this  method 
depends  principally  on  the  quality  of  the  lead  and  the 
quantity  of  silver  in  it.  The  process  will  succeed  if  the 
lead  is  free  from  other  base  metals.  Antimony  and 
copper  aggravate  the  formation  of  crystals,  from  which 
the  liquid  lead  separates  with  difficulty.  The  produc- 
tion of  pure  lead,  also  an  object  of  this  method,  cannot 
be  obtained  in  that  case.  If,  therefore,  such  impure  lead 
is  designed  for  crystallization,  it  must  be  subjected  first 
to  purification,  causing  thus  expense  and  loss  in  metals. 
This  purification  of  impure  lead,  especially  if  antimony 
is  present,  may  be  executed  by  melting  it  in  a  reverb- 


PKOCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  167 

eratory  furnace  at  a  very  low  temperature,  keeping  it 
for  some  time  in  such  condition.  It  forms  then  a  crust 
on  the  surface,  which  principally  consists  of  oxyd  of  lead 
and  antimonate  of  oxyd  of  lead.  This  crust  must  be 
drawn  off  as  long  as  it  appears,  or  stirred  by  increased 
heat  with  addition  of  lime  and  charcoal  dust,  by  which 
a  great  part  of  the  lead  is  reduced  again.  But  it  is 
evident  that  under  such  circumstances,  even  when  the 
purest  lead  would  result  from  subsequent  crystallization, 
a  direct  cupellation  in  California  and  Nevada  Territory 
is  more  advantageous,  and  that,  if  the  cupellation  on 
account  of  too  small  amount  of  silver  would  not  pay, 
the  crystallization,  depending  on  the  purification  of 
lead,  would  pay  still  less. 

If  the  lead  is  not  overloaded  with  base  metals,  but 
containing,  however,  so  much  as  to  interfere  with  the 
crystallization,  a  more  simple  refining  may  be  adopted. 
The  lead  is  introduced  into  a  Pattinson  kettle  melted 
and  stirred  with  a  wooden  rod,  by  which  the  lead  is 
brought  into  a  turbulent  motion,  exposing  always  a 
renewed  surface  to  the  air,  promoting  thus  the  oxyda- 
tion  of  the  base  metals.  The  impurities  are  drawn  off, 
till  they  cease  to  appear. 

The  number  of  kettles  required  for  crystallization 
is  determined  principally  by  the  amount  of  silver.  The 
process  offers  the  best  advantage,  if  the  lead  contains 
from  five  to  ten  ounces  per  ton.  In  this  case,  a  few 
crystallizations  render  two  kinds  of  lead,  one  poor,  the 
other  rich ;  the  latter  ready  for  cupellation.    At  a 


168  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

higher  amount  of  silver  the  process  is  prolonged,  caus- 
ing more  expense  for  fuel  and  labor ;  but  under  favor- 
able circumstances,  for  instance,  if  very  pure  lead  is 
obtained  which  would  command  a  better  price,  then 
also  lead  containing  from  fifty  to  sixty  ounces  per  ton 
could  be  advantageously  subjected  to  the  concentration 
process. 

The  degree  to  which  the  concentration  is  carried  on 
is  important,  because,  besides  the  increased  expense  for 
labor  and  fuel,  a  very  rich  lead  produces  a  richer  lith- 
arge when  cupelled.  The  concentration  accordingly 
ought  not  to  exceed  four  or  five  hundred  ounces  per 
ton. 

Lead,  containing  silver  in  such  small  proportion  as 
will  not  pay  the  expense  of  cupellation,  can  be  worked 
advantageously  by  way  of  crystallization.  The  low 
temperature  does  not  much  affect  the  lead,  and  besides 
when  the  lead  is  pure  the  loss  in  silver  is  insignifi- 
cant. The  loss  of  lead  in  England,  which  is  generally 
pure,  amounts  to  two  per  cent.  Other  qualities  of  lead, 
in  Germany,  suffer  a  loss  of  three  per  cent.,  while  the 
loss  in  cupellation  and  the  reduction  of  litharge  amounts 
to  from  eight  to  ten  per  cent.  Generally  there  is  no 
gain  on  fuel  or  labor  in  this  process,  compared  with 
cupellation.  If  there  is  a  considerable  amount  of  silver 
in  the  lead,  the  crystallization  may  be  even  more 
expensive,  but  the  gain  in  lead  may  cover  the  differ- 
ence and  leave  also  a  profit.  This,  however,  depends 
on  the  price  of  lead. 


CHAPTER  VI. 


DESCRIPTION  OF  MACHINEEY  AND  FURNACES. 


COMMON  IRON  PAN. 

Sec.  49.  Fig.  22  represents  a  common  iron  six-foot 
pan.  Fig.  23  is  a  vertical  section  of  Fig.  22  on  the  line 
A  B ;  a  shows  a  wooden  cross,  to  which  the  wooden 
block,  b,  with  the  iron  shoes,  c,  are  fastened  by  the  bolts, 
d.  Each  shoe  has  a  pin,  e,  about  one  inch  long,  fitting 
in  the  wooden  block,  in  order  to  prevent  movement. 

On  the  shaft,  y,  is  the  yoke,/,  fastened  by  a  key.  The 
two  ends  of  the  yoke  fit  in  the  holes,  h,  of  the  cross,  a, 
but  not  too  tight,  so  that  the  muller  can  follow  the  wear 
of  the  shoes.  Pans,  having  the  gear  underneath,  and 
the  shaft  through  the  cone,  are  so  arranged  that  by 
means  of  a  screw  the  muller  can  be  raised.  This  ar- 
rangement for  raising  the  muller  is  not  important,  as 
the  muller  generally  grinds  with  its  full  weight.  The 
steam  is  introduced  into  the  pulp,  through  the  pipe,  I; 
k,  Jc,  are  the  discharge  pipes ;  m  represents  the  false  bot- 


170  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

torn,  made  of  one  piece,  two  inches  thick.  This  bottom 
must  be  one  inch  less  in  diameter,  so  that  half  an  inch 
of  free  space  is  left  between  the  bottom  and  the  pan  on 
the  sides,  and  on  the  cones.  The  best  way  to  fasten 
these  bottoms,  and  also  to  prevent  the  quicksilver  from 
getting  under  them,  is  the  following :  Strips  of  strong 
cloth,  two  inches  and  a  half  wide,  are  laid  over  the 
space  between  the  bottom  and  sides,  which  is  filled  with 
a  paste  of  iron  filings  and  wedged  with  well  dried 
wooden  wedges,  quite  close  together,  so  that  the  cloth 
is  equal  in  height  on  both  sides  of  the  wedges,  which 
are  driven  in  tight.  The  wedges  must  be  a  little  shorter 
than  the  thickness  of  the  false  bottom,  leaving  thus  a 
space  above  them,  which  is  covered  with  a  paste  of  iron 
filings. 

WHEELER'S  PAN. 

Sec.  50.  Fig.  24  shows  the  ground  view  of  the  pan, 
and  Fig.  25  the  vertical  section  of  Fig.  24,  on  the  line 
A  B.  For  the  sake  of  clearness  of  representation,  the 
yoke,  a,  and  the  guide-blade  arrangement,  g,  b\  b,  c,  of 
Fig.  25,  are  not  represented  in  Fig.  24,  but  the  position 
of  the  guides  is  shown  by  dotted  lines,  c.  The  muller, 
J,  and  the  ring,  e,  (the  two  journals  of  which  move  in  the 
box,/,  fixed  to  the  muller,  while  the  other  two,  g,  move 
in  the  box,  h,  of  the  yoke,  a)  cover  only  half  of  the  pan, 
Fig.  24.  The  other  half  shows  the  dies,  i;  laid  directly 
on  the  bottom  of  the  pan,  k    They  are  kept  in  place 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  171 

in  the  centre  by  the  ring,/,  and  on  the  sides  by  the  in- 
clined ledges,  I  Each  die  has  for  this  purpose  a  projec- 
tion, m,  which  is  placed  under  the  ledge,  I,  with  the 
beveled  side,  as  represented  in  Fig.  25,  m\  The  dies 
are  one  inch  thick,  beveled  on  each  long  side  in  the 
same  direction,  so  that,  in  putting  them  together,  the 
groves,  i\  are  formed. 

In  Fig.  25  the  muller,  d,  shoe,  n,  and  die,  i,  are  repre- 
sented on  one  side.  The  muller  has  twelve  oblong 
openings,  d%  two  and  one-fourth  inches  wide  by  ten 
and  three-fourths  long.  One  of  the  long  sides  towards 
the  dies  is  beveled,  as  shown  by  the  dotted  lines,  s.  The 
projection  on  the  shoes  is  of  the  same  shape,  being  only 
half  an  inch  narrower  and  as  much  shorter,  so  that  the 
space  of  half  an  inch  is  wedged  with  dry  pine  wood,  n% 
by  which  the  shoe  is  fastened  to  the  muller.  The  shoe 
below  the  muller  is  represented  by  the  dotted  lines  o. 
On  the  outer  ledge  of  the  muller  are  inclined  ledges, 
o%  which,  in  connection  with  those  of  the  pan,  I,  create 
an  upward  current  of  the  pulp ;  c,  c,  are  guide-blades  con- 
veying the  pulp  to  the  centre.  These  guides  have  at 
the  outer  end  a  projection,  like  a  hook,  as  indicated  by 
the  dotted  lines  c,  c.  This  hook  catches  the  blade,  p, 
which  is  also  bent  hook-like,  fastened  to  the  pan  by  an 
iron  wedge,  between  the  ribs,y.  Thus  the  guides 
resist  the  current  of  the  pulp. 

The  guide-blades,  c,  are  connected  with  the  frame,  q, 
formed  of  four  rods,  screwed  to  the  ring,  b%  which  again 
is  in  connection  with  the  lower  ring,  b,  by  four  bolts,  to 


172  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

which  the  guides  are  attached.  The  frame  rests  by 
means  of  the  screw,  q\  on  the  shaft,  r,  and  can  be  raised 
or  lowered. 

a  is  the  steampipe,  conveying  the  steam  directly  into 
the  pulp ;  u  shows  the  steam  chamber,  if  the  pulp  is  to 
be  heated  through  the  bottom.  This,  however,  has 
proved  unnecessary,  and  it  consumes  more  fuel.  On 
that  account  no  more  pans  of  this  kind  are  made  with 
a  steam  chamber.  As  a  consequence,  the  arrangement 
with  the  box,  t,  is  also  altered,  and  affords  more  conve- 
nience in  oiling  and  handling ;  w  and  u?  show  the  appa- 
ratus for  raising  the  muller.  By  screwing  the  rod,  y,  the 
muller  will  be  raised  gradually,  but  if  a  sudden  lift  is 
required,  the  rod  must  be  pushed  down. 

The  dies,  as  well  as  the  bottom  of  the  pan,  are  not  so 
perfect  as  to  fit  exactly  without  giving  way  a  little  in 
one  place  or  another,  thus  presenting  an  uneven  grind- 
ing surface,  and  causing  a  jarring  for  many  hours  after 
starting.  To  avoid  this,  some  wet,  muddy  tailings,  or 
ore,  is  introduced  into  the  pan  and  spread  uniformly, 
nearly  half  an  inch  deep.  Each  die  is  then  laid  in  the 
proper  radial  direction,  the  projection  of  the  outer  end 
under  the  ledge,  I,  and  imbedded  well  into  the  mud,  till 
it  lies  solid  and  level.  Care  must  be  taken  that  the 
stump  edge  1,  Fig.  24,  does  not  project  over  the  sharp 
edge  2  of  the  next  die.  When  all  twelve  dies  are  set 
in,  the  collar,  /,  is  put  over  the  heads  of  the  dies,  and 
fastened  by  turning  it  under  the  nuts  of  the  centre- 
piece 3.    The  spaces,  V  and  Ic,  are  filled  with  wet  ore, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  173 

level  with  the  surface  of  the  dies,  and  the  muller  placed 
over  them. 

Some  water  is  poured  over  the  muller,  then  some 
diluted  mud,  and  allowed  to  rest  for  about  two  hours 
before  starting,  in  order  to  effect  the  swelling  of  the 
wedges,  n\ 

Above  the  pans  a  sliding  block  is  required,  for  the 
purpose  of  lifting  the  muller.  The  muller  must  be 
lifted  at  least  once  every  week,  and  pan  and  muller 
cleaned  from  adhering  amalgam,  which  accumulates 
round  the  centrepiece,  preventing  the  ore  from  passing 
freely  under  the  muller.  The  first  three  or  four  charges 
require  two  or  three  hours'  longer  grinding,  on  account 
of  the  roughness  of  the  shoes  and  dies.  These  pans  are 
made  in  the  Miners'  Foundry,  San  Francisco. 

WHEELER'S  AGITATOR. 

Sec.  51.  Fig.  26  represents  a  vertical  section  of  the 
agitator  (exclusive  of  the  arms,  a,  which  are  shown  in  a 
front  view).  The  upright  shaft,  b,  is  hollow  for  the 
purpose  of  conveying  the  water  through  the  arms  a,  of 
which  there  are  four,  into  the  pulp,  in  order  to  dilute  it 
for  an  easier  separation  of  the  amalgam  from  the  sand. 
If,  however,  it  is  treated  as  described  in  Sec.  27,  no 
dilution  is  required,  therefore  the  hollow  shaft  and  arms 
are  superfluous  and  may  be  replaced  by  solid  ones.  In 
case  the  pulp  is  too  thick,  some  water  may  be  added 
in  the  pan,  several  minutes  before  the  discharge. 


174  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

The  shaft,  b,  slides  in  the  gear,  <?,  on  the  fixed  keys, 
resting  on  the  fork,  d,  and  a  loose  collar,  e.  By  means 
of  the  lever,  d,  and  screw,  /,  the  shaft  can  be  lifted  with 
the  shoes  gradually.  The  cast-iron  bottom,^,  is  inclined 
towards  the  centre,  ending  in  a  bowl,  h,  for  the  reception 
of  quicksilver.  This  bowl  is  kept  always  full  of  mercury 
so  that  when  the  pans  are  discharged  the  superfluous 
quicksilver  runs  out  by  the  siphon,  L  The  three-eighth 
pipe,  k,  four  inches  above  the  bottom,  carries  out  the 
tailings  constantly,  being  diluted  with  a  one-inch 
stream,  m,  of  clear  water.  The  lower,  one-inch  pipe,  1, 
serves  for  the  discharge,  if  cleaning  is  required;  o  is 
also  a  discharge  hole ;  p  represents  the  shoes ;  they 
are  light  and  fastened  with  bolts  so  that  little  friction 
takes  place ;  q  are  wooden  staves  from  twenty-five  to 
thirty  inches  high. 

Hepburn's  agitator  differs  from  Wheeler's  in  having 
a  level  bottom ;  and  instead  of  the  bowl  in  the  centre, 
there  is  a  circular  groove  near  the  middle  of  the  iron 
bottom,  connected  with  the  siphon.  This  agitator  will 
be  worked  to  the  best  advantage  without  dilution  in 
the  same  way  as  Wheeler's  (Sec.  27). 

HEPBURN  AND  PETERSON'S  PAN. 

Sec.  52.  Fig.  27  represents  a  perpendicular  section 
of  the  ground  view  of  Fig.  28,  on  the  line  A  B.  Fig. 
28  shows  a  ground  view  of  the  pan,  the  centre  piece  of 
which  is  a  horizontal  section  on  the  line  0  D  of  Fig.  27. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  175 

The  pan,  a\  is  eighteen  inches  deep  on  the  side,  and 
twenty-seven  inches  deep  near  the  cone,  b}  forming  thus 
an  inclined  bottom.  The  shaft,  c,  goes  through  the 
hollow  cone,  b.  The  cylindrical  driver,  d,  is  fixed  to 
the  shaft  by  a  stationary  key.  The  muller,  m,  has  three 
stands,  e%  joining  in  one  piece,  e",  in  which  three  open- 
ings, p,  are  made,  for  the  passage  of  the  logs,  e,  of 
the  driver,  d.  When  the  driver  is  set  in,  it  must  be 
turned  to  the  right,  so  that  the  logs,  e,  will  come  under 
the  leveling  screw,  x,  as  represented  in  Fig.  28  by  the 
dotted  lines,  joining  the  logs,  a,  of  the  stand,  e",  whereby 
the  motion  is  transferred  from  the  driver  to  the  muller. 
The  screw,  /,  serves  for  raising  the  muller.  The  nut,  o,  is 
movable  inside  of  the  driver,  but  is  fixed  in  the  hand- 
wheel,  h,  so  that  the  motion  of  the  screw,  /,  can  be 
arrested  by  holding  the  handwheel,  h.  Holding  this 
handwheel,  the  muller  can  be  raised  when  in  motion, 
by  the  screw,  /,  with  the  upper  hand-wheel,  h\  The 
upper  part  of  the  cone,  which  serves  as  a  box  for  the 
shaft,  c,  is  lined  with  babet  metal,  z.  The  shoes,  n,  are 
fastened  to  the  muller  by  the  bolt,  mJ ;  there  are  also 
two  pins  on  each  shoe,  which  fit  in  small  holes  of  the 
muller,  to  prevent  motion.  In  Fig.  28,  these  shoes 
are  shown  by  dotted  lines.  The  dies,  i,  have  two  pro- 
jections on  the  lower  side.  The  projections  fit  into 
corresponding  grooves  of  the  pan  bottom.  A  wedge,  r, 
fastens  the  die  in  its  place.  The  pipe,  q,  serves  for  the 
discharge,  and  q'  for  conveying  steam. 

These  pans  are  furnished  by  the  Vulcan  Foundry, 
San  Francisco. 


176  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


ROASTING  FURNACE. 

Sec.  53.  The  roasting  furnace,  represented  by  Fig. 
29,  the  horizontal  section  of  Fig.  30  on  the  line  CD; 
then  Fig.  30,  a  vertical  section  of  Fig.  29  on  the  line 
A  B  shows  the  right  proportion  and  dimensions  of  an 
economical  furnace  in  regard  to  fuel  and  time  of  roast- 
ing. The  hearth-bottom,  a,  is  made  carefully  of  the 
hardest  bricks,  laid  edgewise  as  close  as  possible.  Bricks 
with  uneven  sides  must  be  rejected ;  b  shows  a  square 
hole  in  the  floor  for  discharging  the  roasted  ore.  The 
flue,  c,  communicates  with  the  holes,  c\  in  the  arch,  v, 
nine  inches  in  diameter ;  they  being  perpendicular,  are 
not  liable  to  be  choked  by  the  ore;  d  is  a  canal  for 
the  purpose  of  cleaning  c.  The  distance  between  the 
arch  and  bottom  near  the  bridge,  g,  is  twenty-one  inches, 
but  near  the  flue,  c\  only  eight  inches.  The  flue,  c,  can 
be  led,  either  under  the  floor,  or  directly,  or  through 
dust  chambers,  into  a  chimney,  which,  for  one  furnace, 
must  be  twenty-five  or  thirty  feet  high,  with  the  inside 
from  sixteen  to  eighteen  inches  square.  On  top  of  the 
chimney  an  iron  cover,  controlled  by  a  chain,  regulates 
the  draft  of  the  furnace ;  e  represents  an  iron  funnel, 
big  enough  to  receive  one  charge  of  ore.  It  is  fitted 
tight  to  another  small  cast-iron  funnel  with  an  opening 
of  about  four  inches,  with  a  slide,  L  The  canals,  /,  are 
draft  holes  for  the  purpose  of  drying  the  brick  work. 

As  the  temperature  does  not  amount  to  white  heat, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  177 

common  bricks  are  generally  used  for  roasting  furnaces. 
There  are  often,  however,  such  bricks  which  cannot 
stand  even  the  roasting  heat,  especially  in  the  fire- 
place. New  bricks,  therefore,  must  be  examined  first 
by  exposing  one  to  light  red  heat  for  an  hour  or  so. 

The  bridge,  g.  is  the  part  most  exposed  to  injury 
by  fire  on  one  side,  and  by  stirring  with  hoes  on  the 
other.  It  is  of  great  advantage  to  make  the  bridge  of 
one  or  two  pieces  of  some  kind  of  sandstone,  granite  or 
conglomerate,  which  does  not  burst  on  being  heated. 

The  furnace  must  be  well  tied  with  iron  rods,  k,  and 
uprights,  I.  In  some  places,  the  uprights  are  made  of 
wood,  six-by-six  or  six-by-eight.  A  new  furnace  must 
be  dried  carefully.  It  requires  five  or  six  days*  slow 
fire.  Upon  this  first  drying  the  durability  of  the  arch 
depends.  The*  furnace  must  always  be  red-hot  before 
the  first  charge  of  ore  is  introduced. 

MECHANICAL  ROASTING  FURNACE. 

Sec.  54.  Fig.  31  represents  a  vertical  section  of  a 
mechanical  furnace.  The  iron  hearth-frame,  a,  twelve 
feet  in  diameter,  has  sides  ten  inches  high.  The  fire 
tiles,  b,  are  first  laid,  then  the  four-inch  bottom,  c,  formed 
by  two  rows  of  bricks ;  d  is  the  discharge  opening, 
three  feet  three  inches  long,  four  inches  wide,  with 
iron  door  on  hinges  below.  The  funnel,  e,  conveys 
the  discharged  ore  through  the  hole,/,  outside  of  the 
furnace.  The  hearth  is  set  in  motion  by  the  cog-wheel, 
12 


178  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

g.  Five  or  six  revolutions  will  be  sufficient.  The 
hearth  revolves  on  eight  rollers,  h,  and  on  the  balls,  h\ 
The  pin,  i,  prevents  any  motion  sideways.  The  fire 
tiles,  k,  on  the  bridge  are  placed  close  to  the  hearth. 
The  cast-iron  pipe,  /,  rests  outside,  independent  of  the 
furnace,  on  both  sides.  It  lies  above  the  centre  of  the 
hearth.  This  pipe  (three  and  one-half  by  two  inches 
inside)  cooled  by  a  constant  stream  of  water,  withstands 
destruction  by  heat,  cooling  also  the  iron  stirrers,  n. 
There  are  eight  or  ten  of  these  stirrers  on  the  pipe,  so 
arranged  that  while  one-half  of  them  turn  the  ore  to 
the  right,  the  other  half  in  a  reversed  position  throw 
it  to  the  left.  The  doors,  m  (on  each  side),  must  be 
wide  enough  to  allow  the  taking  out  and  replacing  of 
the  stirrers.  This  can  also  be  effected  by  the  other 
door,  o.    The  flue,  jp,  is  indicated  by  dotted  lines. 

The  ore  is  introduced  as  usual  by  the  funnel,  p\  while 
the  furnace  is  red-hot  and  the  hearth  revolving.  After 
roasting,  the  hearth  is  stopped,  the  door  of  the  discharge 
hole,  d,  opened,  and  the  hearth  started  again.  When 
the  ore  is  discharged,  the  door  must  be  closed  and  the 
space,  d,  filled  with  roasted  ore. 

THE  RETORT. 

Sec.  55.  The  retort,  Fig.  20,  represents  a  front  view 
without  the  door.  Fig.  21  is  a  vertical  cut  of  Fig.  20  on 
the  line  A  B,  being  shut  by  the  door  or  cover,  a.  The 
retort  is  made  of  cast-iron,  four  feet  long,  eleven  inches 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  179 


wide  and  nine  inches  high.  The  retort  has  two  wings, 
b,  as  long  as  the  retort,  on  which  it  rests  on  the  mason 
work,  so  that  three  inches  on  each  side,  d,  are  left  clear. 
The  flame,  on  account  of  the  wings,  will  play  round  the 
lower  part  of  the  retort,  passing  the  space,  c,  then/ 
above  the  retort,  escaping  through  g.  The  fire-place,  h, 
has  grates  two  feet  long,  and  may  be  according  to  the 
fuel  either  three  feet  long  or  shorter,  as  indicated  by 
the  dotted  line,  i  The  condensing  pipe,  k,  is  furnished 
at  the  end  with  a  funnel,  I.  A  sheet-iron  pipe,  m,  rests 
on  the  funnel,  made  tight  by  some  clay  or  mud  inside. 
Through  the  lead  pipe,  n,  a  constant  stream  of  cold 
water  flows  to  the  funnel,  then  round  the  pipe,£,  up  and 
out  at  o.  The  funnel  is  wrapped  with  cloth,  p,  which 
reaches  into  the  water.  The  water  level,  q,  must  be 
kept  about  half  an  inch  below  the  funnel. 


THE  CRUCIBLE  FURNACE. 

Sec.  56.  This  furnace  is  very  simple.  Fig.  13  is  a 
vertical  section  of  Fig.  14  on  the  line  A  B:  Fig.  14 
represents  a  ground  view.  This  furnace,  calculated  for 
the  black-lead  crucible  No.  40,  is  fifteen  inches  square, 
lined  with  fire  brick ;  a  shows  the  slide  doors,  c  the 
cast-iron  plate  with  the  rib,  d,  to  support  the  doors,  a. 
The  crucible,  e,  stands  on  a  piece  of  fire  brick  on  the 
grate,  /,  which  consists  of  movable  iron  rods ;  g  is  the 
ash-pit,  having  a  very  tight  floor,  or  a  cast-iron  plate 
with  a  rim  on  three  sides. 


180  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


A  round  or  circular  furnace  for  the  same  size  of 
crucible  must  be  eighteen  inches  diameter  in  the  clear. 
As  a  matter  of  course  this  furnace  will  serve  also  for 
smaller  sizes  of  crucibles. 

THE  MELTING  FURNACE. 

Sec.  57.  Fig.  33  represents  a  horizontal  section 
on  the  line  A  B  of  Fig.  32,  which  is  a  vertical  cut  on 
CD  of  Fig.  33.  Another  vertical  cut  on  the  line  E  F 
is  shown  in  Fig.  34.  The  cast-iron  pan,  a,  is  thirty-seven 
inches  in  diameter  and  fifteen  inches  deep.  This  pan 
serves  for  the  reception  of  the  fire-proof  material,  e, 
forming  the  crucible.  This  pan  has  a  tap-hole,  b,  close 
to  the  bottom  about  six  inches  in  diameter.  On  one 
side  near  the  rim,  the  pan  has  a  shoulder,  c,  on  which 
the  flue-plate,  d,  rests. 

The  pan,  a,  is  placed  on  bricks,  g,  about  four  inches 
apart  so  that  air  canals,  h,  are  formed,  for  the  purpose 
of  cooling  the  hearth-mass,  e,  in  the  pan.  The  sides  of 
the  pan  are  also  exposed  to  the  cooling  air.  The  flue- 
plate,  d,  has  a  pitch  of  about  thirty  degrees.  The 
hearth,  e,  is  beaten  to  six  inches  above  the  edge  of  the 
pan,  in  which  a  crucible  twelve  inches  deep  is  cut  out 
with  a  curved  blade,  so  that  under  the  crucible  in  the 
centre,  the  mass  is  about  six  inches  thick ;  %  represents 
the  feed  door,  through  which  the  ore  is  introduced  on 
the  inclined  flue,  I,  whence  the  melting  mass  runs  into 
the  crucible,  /.  The  slag  flows  through  the  canal,  m, 
three  inches  wide  and  nearly  four  inches  deep. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  181 

The  tap-hole,  b,  is  nine  inches  on  the  outside,  ending 
in  the  centre  of  the  crucible  with  a  half-inch  hole,  n. 
The  door,  o,  on  the  slag  canal,  m,  serves  for  drawing  off 
the  slag ;  p  shows  the  dust  chamber ;  q  and  q'  openings 
for  the  purpose  of  cleaning  the  chamber.  The  ore 
particles,  striking  against  the  partition,  r,  drop  down, 
forming  masses  of  slag-like  stalactites,  which  must  be 
removed  from  time  to  time. 

The  arch,  x,  formed  of  fire  bricks  (like  all  mason- 
work  coming  in  contact  with  fire),  must  be  taken  off 
when  a  new  crucible  is  required.  The  crucible  may 
last  two  or  three  weeks  according  to  the  material. 

When  all  is  finished,  except  the  roofing,  the  flue- 
plate,  d,  is  lined  first  with  one  row  of  fire  brick,  y, 
after  which  the  hearth-mass  is  beaten  in  the  pan  in 
the  following  way :  the  mass  is  prepared  of  fire-proof 
material,  either  of  fire-brick  previously  used,  carefully 
cleaned  from  slag,  pulverized,  and  three  parts  of  it  (in 
volume)  mixed  with  one  part  of  good  clay,  or  three 
parts  of  pure  white  quartz  with  one  part  clay  ;  or  three 
parts  burnt  fire-proof  clay  with  one  part  unburnt  will 
answer  the  purpose.  The  materials  have  to  be  crushed 
dry  and  sifted  through  a  sieve  of  sixty-four  holes  to 
the  square  inch.  After  being  well  mixed,  the  stuff  is 
sprinkled  over  with  water  while  it  is  shoveled  on  a 
clean  floor.  The  shoveling  must  be  performed  with 
much  diligence,  from  one  side  to  the  other  in  order  to 
have  the  whole  mass  uniformly  moist. 

The  quantity  of  water  must  be  found  out  by  the 


182  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

appearance  of  the  mass.  A  handful  of  it,  squeezed  hard, 
must  form  a  ball,  which  may  be  handled  gently,  but  it 
should  crumble  to  its  former  state  under  a  pressure  of 
the  fingers.  With  this  prepared  mass  the  pan,  a,  is 
charged  about  six  inches  deep,  leveled,  and  by  one  or 
two  men  beaten  in,  by  means  of  iron  bars  of  about 
twenty  pounds  weight  and  five  feet  long,  having  at  one 
end  exactly  the  size  and  shape  of  a  hen's  egg  at  the 
larger  end.  The  men  commence  to  beat  the  hearth  in  the 
centre,  pursuing  a  spiral  course,  stamping  with  the  egg- 
point  in  a  perpendicular  line,  by  a  lift  of  about  eight 
inches,  striking  with  the  rod  close  to  each  preceding 
stroke.  When,  by  a  screw-like  advance,  the  stamping 
has  reached  the  side  of  the  pan,  it  can  be  carried  on 
back  to  the  centre  in  the  same  way,  then  again  to  the 
side  and  so  on,  till  about  two  inches  loose  mass  remains. 

If  a  hole  can  be  scratched  easily  with  the  finger  into 
the  stamped  mass,  the  rod  must  be  used  with  more 
force.  Another  charge  of  the  same  quantity  of  stuff  is 
introduced  as  before.  Care  must  be  taken  to  have 
always  two  inches  of  loose  mass  above  the  stamped, 
before  the  next  charge  is  put  in.  If  the  whole  mass 
be  beaten  hard,  the  next  charge  cannot  unite  with  the 
underlayer  perfectly.  The  beating  on  the  second 
charge  is  executed  in  the  same  way  as  before  and  so 
on,  till  the  hard-beaten  mass  stands  about  two  inches 
above  the  line  v,  extending  into  the  flue  as  far  as  shown 
by  the  drawing.  The  hearth-mass  in  the  flue,  /,  must  be 
stamped  with  lighter  wooden  stamps  of  the  shape  of 
the  iron  ones. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  183 

The  hearth  is  then  cut  level,  as  indicated  by  the  line, 
v,  and  the  surface,  I,  in  the  flue.  After  this,  the  crucible, 
/,  must  be  first  cut  roughly  with  a  hatchet  or  a  similar 
instrument,  but  the  finishing  to  the  proper  size  and 
shape  is  done  with  a  curved  blade.  The  tap-hole,  b,  is 
cut  out  as  represented  in  Fig.  34. 

When  this  is  done,  the  arch  and  binding  of  the  furnace 
will  finish  the  work.  It  is  now  important  to  dry  the 
hearth  carefully.  It  is  very  advantageous  to  cover  the 
surface  of  the  crucible  about  three  inches  thick  with 
ashes  in  order  to  prevent  the  direct  action  of  the  fire 
on  the  mass.  After  three  or  four  days'  drying,  the 
fire  may  be  increased  by  degrees,  so  that  the  furnace 
becomes  red-hot  after  five  or  six  days'  drying. 

The  chimney  should  be  forty  or  fifty  feet  high,  from 
eighteen  to  twenty  inches  square  in  the  clear,  and  lined 
with  fire-bricks. 

The  fire-place,  Hy  is  calculated  for  coal 

CUPELLING  FURNACE. 

Sec.  58.  The  cupelling  furnace  is  represented  by 
Fig.  35,  which  is  the  vertical  section  of  Fig.  36  on  the 
line  A  B.  Fig.  36  shows  the  horizontal  cut  of  Fig.  35 
on  C  D.  The  brick-work,  b,  is  one  foot  eight  inches 
above  the  floor.  On  this  block  are  laid  rows  of  bricks,  c, 
forming  channels,  d,  for  the  free  circulation  of  air.  On 
the  brick  bridges  a  cast-iron  pan  is  placed  for  the  recep- 
tion of  the  hearth-mass. 


184  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

This  pan  is  four  feet  in  diameter  with  a  throat,  /,  ten 
inches  long  and  twelve  inches  wide.  The  bottom  is 
perforated  with  several  holes,  each  half  an  inch  in  the 
clear,  for  the  easy  escape  of  moisture.  This  pan  is  eleven 
inches  deep ;  g  is  a  cast-iron  plate  on  which  the  litharge 
falls ;  i  represents  a  fire-tile  on  which  the  lead  bars  are 
placed ;  it  is  a  little  inclined  towards  the  test,  Jc.  The 
opening,  I,  is  for  the  nozzle  of  a  pair  of  bellows.  The 
nozzle,  a,  Fig.  37,  is  also  inclined  at  such  a  degree  that 
the  stream  of  air  may  touch  as  much  of  the  surface  of 
the  bath  as  possible.  A  continual  stream  of  air  pro- 
duced by  a  fan  answers  the  purpose  better  than  a  forge- 
bellows  ;  n  is  the  opening  above  the  litharge-bridge,  /. 
Through  this  opening  the  lead  vapors  and  all  burning 
products  escape. 

The  arch,  o,  is  made  of  common  bricks  and  must  be 
removed  as  often  as  a  new  test  is  required.  Larger 
furnaces  are  provided  with  a  movable  arch,  formed  of 
sheet-iron  or  flat  wrought-iron,  lined  with  clay  inside. 
By  means  of  a  crane  the  arch  can  be  raised  and  turned 
to  one  side. 

If  the  mass,  e,  forming  the  hearth,  is  composed  of 
wood  ashes,  it  causes  much  trouble  in  cupelling.  Bone- 
ash  is  an  excellent  material,  but  too  expensive.  The 
most  proper  material  is  marl.  If  this  cannot  be  obtained, 
a  composition  of  pulverized  lime-rock  and  clay  will 
answer  perfectly.  For  this  purpose  one  part  of  clay,  or 
in  the  absence  of  it,  light  yellow  loam  is  mixed  with 
three  parts  of  lime-rock,  all  well  dried  and  pulverized. 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  185 

This  mass  must  'be  sifted  through  a  sieve  of  about  one 
hundred  holes  to  the  square  inch,  then  sprinkled  with 
water  and  prepared  as  described  in  Sec.  57. 

The  pan,  a,  is  then  charged  about  six  inches  deep 
with  the  prepared  hearth-mass,  after  the  front  opening 
has  been  shut  up  securely  in  some  way,  for  instance,  by 
bracing,  as  indicated  by  x.  One  or  two  men  commence 
to  stamp  the  mass  in  the  centre  with  wooden  or  iron 
stamps  of  the  same  size  and  shape  as  described  in 
Sec.  57. 

The  stamping  goes  on,  till  the  hearth  is  beaten  about 
three  inches  below  the  rim,  when  a  cast-iron  ring  of  the 
size  and  shape  of  the  pan,  but  with  sides  only  six  inches 
high  is  placed  rim  to  rim,  corresponding  on  the  pan,  as 
indicated  by  the  dotted  line,  2,  Fig.  35.  Some  more 
mass  is  then  introduced,  and  the  stamping  continued 
till  the  hearth  is  formed  hard  two  or  three  inches  above 
the  rim  of  the  pan,  a. 

The  mass  is  then  cut  with  a  knife  around  the  ring 
down  to  the  pan's  edge,  in  order  to  prevent  the  break- 
ing of  the  mass  when  the  ring  is  removed.  The  hearth 
is  cut  level  with  the  line,  p,  then  the  test,  k,  five  inches 
distant  from  the  rim,  with  a  curved  knife.  This  is  six 
inches  deep  and  four  feet  diameter.  The  litharge- 
bridge,  /,  should  be  cut  inclined,  as  represented  by  r. 

When  this  is  finished,  the  arch  can  be  formed  and 
the  furnace  slowly  dried. 

The  cast-iron  pan,  a,  offers  great  advantages  in  the 
preservation  of  the  test,  in  less  danger  in  drying  and 


186  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

in  withstanding  the  heat  longer,  which  has  less  influence 
on  the  mass,  being  cooled  from  beneath. 


THE  REFINING  FURNACE. 

Sec.  59.  For  the  purpose  of  refining  silver  or  melting 
retorted  amalgam,  the  furnace,  Figs.  32,  33,  will  answer 
perfectly,  changing  a  few  dimensions.  The  fire-place, 
E,  if  intended  for  dry  wood,  should  be  fifteen  inches 
wide  and  three  feet  six  inches  long.  The  crucible,  /, 
should  be  only  six  or  eight  inches  deep,  the  line,  v,  being 
then  one  or  two  inches  above  the  rim  of  the  pan,  a, 
as  represented  by  the  dotted  line,  f\  The  flue,  I,  will 
answer  with  a  length  of  from  twelve  to  fifteen  inches, 
with  a  door,  i\  for  the  purpose  of  introducing  the  silver 
on  the  inclined  plane,  from  which  it  melts  into  the 
crucible.  For  the  hearth-mass,  if  a  purer  sort  of  silver 
is  treated,  the  same  mixture  as  described  for  this  fur- 
nace (Sec.  57)  may  be  used ;  but  in  treating  silver 
which  contains  lead,  or  which  requires  an  addition  of 
lead  for  the  purpose  of  oxydizing  the  base  metals  or 
other  impurities,  the  mixture  of  lime  and  clay  as  used 
for  the  cupelling  furnace  (Sec.  58)  is  preferable. 

There  is  no  flue-plate,  d,  required,  also  no  tap-hole,  as 
it  is  more  convenient  to  dip  the  silver  out  with  an  iron 
ladle  into  moulds. 


PART  SECOND. 


GENERAL  METALLURGY  OF  SILVER  ORES. 


CHAPTER  I. 


DIVISION  AND  ASSAY  OF  SILVER  ORES. 

Sec.  60.  Silver  ores  extensively  used  for  extraction 
are  generally : 

1.  Those  in  which  the  silver  appears  as  one  of  the 
principal  metals.    To  this  class  especially,  belong : 

Native  silver,  containing  sometimes  as  much  as  three 
per  cent,  of  antimony,  arsenic  or  iron. 

Antimonial  silver  with  seventy-seven  or  eighty-four 
per  cent,  of  silver. 

Tellurid  of  silver  with  sixty-one  per  cent,  of  silver, 
containing  sometimes  gold  and  traces  of  iron. 

Silver  glance  with  eighty-seven  of  silver. 

Brittle  silver  ore  with  seventy,  light-red  silver  ore 
with  sixty-five,  and  dark-red  silver  ore  (rubysilver)  with 
fifty-nine  per  cent,  of  silver. 

Silver  fahlerz  with  from  eighteen  to  thirty-one  per 
cent,  of  silver  and  from  twenty-six  to  fifteen  per  cent, 
of  copper  ;  light-gray  silver  ore"  containing  5*7  per  cent, 
of  silver,  thirty-eight  of  lead  and  traces  of  copper.  The 


190  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

gray  silver  ore  from  Freiberg  (Saxony)  has  from  29*73 
to  32*69  per  cent,  of  silver. 

Stromeyerite  (silver-copper  glance),  fifty-three  silver 
and  thirty-one  copper. 

Polybasite  with  from  sixty-four  to  seventy-two  silver, 
and  ten  to  three  copper. 

2.  Such  ores,  in  which  the  small  and  variable  amount 
of  silver  appears  with  other  useful  or  not  useful  metals. 

Sulphuretted  minerals  are  always  rich  in  silver,  than 
the  oxydized.  The  ferriferous  sulphides  are  the  poorest, 
then  follow  sulphides  of  zinc,  of  lead  and  then  those  of 
copper. 

To  this  class  belong : 

a.  Argentiferous  Lead  Ores. 

Sulphuret  of  lead  or  galena  containing  generally  from 
O03  to  0*01  per  cent,  of  silver;  often  also  0*5,  but 
seldom  one  per  cent.  In  some  cases,  however,  galena 
is  found  to  contain  as  much  as  seven  per  cent,  of  silver. 
The  amount  of  silver  in  this  ore  varies  much  even  in 
the  same  mine.  Fine-grained  galena  is  generally  richer 
than  coarse-grained  or  crystallized,  although  in  Arizona 
the  latter  proves  to  be  richer  than  the  fine-grained. 

Carbonate  of  lead  is  generally  found  poor  in  silver. 

b.  Argentiferous  Copper  Ores. 

Fahlerz  (gray  copper) 'contains  traces  of  silver  up  to 
thirty-one  per  cent. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  191 

Copper  pyrites,  purple  copper  and  copper  glance  are 
poor  in  silver.  In  such  cases  the  silver  is  extracted 
only  when  this  ore  occurs  in  company  with  lead  ore, 
but  in  some  cases  the  sulphide  of  copper  and  the  sul- 
phuret  of  silver  form  much  richer  combinations  than 
the  sulphuret  of  lead. 

c.  Argentiferous  Zinc  Ores. 

The  zincblende  (sulphuret  of  zinc)  contains  traces  of 
silver  up  to  0*88  per  cent.  The  carbonate  of  zinc  shows 
onlv  traces. 

d.  Argentiferous  Iron  and  Magnetic  Pyrites, 

Antimonial  and  arsenical  ores,  then  bismuth,  cobalt 
and  nickel  ores  are  poor  in  silver. 

The  ores  of  the  first  class  are  seldom  found  in  large 
quantities  or  massive.  They  are  generally  disseminated 
in  coarser  or  finer  particles  through  the  gangue,  and  in 
that  case  circumstances  of  the  locality  will  decide 
whether  it  is  more  advantageous  to  concentrate  the  ore, 
or  to  save  the  loss  of  silver  suffered  by  concentration, 
and  to  beneficiate  a  larger  bulk  with  more  expense. 

The  ores  of  the  second  class  require  particular  atten- 
tion, partly  as  to  a  close  separation  of  the  different 
metals  in  regard  to  concentration,  and  partly  in  relation 
to  a  suitable  mode  of  extraction  for  each  kind  of  ore. 

Sec  61.    To  find  out  the  amount  of  silver  in  the  ore, 


192  PEOCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


there  are  two  different  tests  in  use  :  the  dry  or  fire 
assay,  and  the  wet  assay.  In  the  fire  assay  the  silver 
of  the  ore  is  fast  taken  up  by  the  lead  and  then  separ- 
ated by  cupellation.  In  consequence  of  volatilization 
and  oxydation  of  the  silver,  the  dry  assay  suffers  a  cer- 
tain loss.  The  oxyd  of  silver  with  that  of  lead  draws 
into  the  cupel  mass,  and  loss  increases  with  the  larger 
amount  of  silver;  but  if  the  lead  is  not  rich,  the  loss  can 
hardly  be  determined  by  the  balance.  The  loss  by 
cupellation  will  also  increase  if  too  much  heat  is  applied. 
Assaying  poorer  ore,  and  using  proper  heat,  the  loss  of 
silver  is  generally  not  taken  into  account;  but  if  rich 
alloys  are  assayed,  the  loss  of  cupellation  must  be  added 
to  the  weight  of  the  button,  according  to  tables  con- 
taining such  losses,  the  results  of  careful  experiments. 

Small  amounts  of  silver  are  easier  and  more  surely 
found  by  the  dry  than  by  the  wet  assay,  but  the  latter 
offers  more  exactness  in  rich  alloys.  For  this  reason 
the  wet  assay  is  used  in  the  mints  and  such  offices, 
where  silver  bars  and  rich  alloys  have  to  be  assayed. 

A.    DRY  SILVER  ASSAYS. 

Sec.  62.  As  mentioned  before,  the  dry  assay  is  based 
on  the  combination  of  the  silver  in  the  ore,  with  the 
lead,  which  was  added  either  in  metallic  condition,  or 
as  litharge  or  acetate  of  lead.  All  lead  or  litharge  of 
commerce  contains  some  silver,  but  generally  so  little 
that  its  influence  on  the  assay  is  insignificant.  For 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  193 

important  assays  of  substances  which  contain  but  very 
little  silver,  the  lead  must  be  prepared  from  acetate  of 
lead,  or  the  latter  is  used  directly  after  calcination. 
The  calcined  mass  contains  more  carbon  in  the  acetic 
acid  than  required  for  the  reduction  of  the  oxyd  of 
lead. 

In  most  instances  the  test  contains  foreign  matters, 
which,  to  be  dissolved,  require  fluxes.  As  fluxes,  potash, 
soda,  borax,  salt  (Glauber's)  and  saltpetre  may  be  used. 
For  the  reduction  of  oxyds,  black  flux,  flour  or  charcoal 
dust  will  serve.  During  the  cupellation  of  argentiferous 
lead,  the  lead  is  first  oxydized,  transferring  oxygen  to 
other  base  metals,  the  oxyds  of  which  together  with 
the  litharge,  are  taken  up  by  the  porous  cupel. 

The  following  assays  may  be  distinguished : 

I.   PROCEEDING  FOR  ORES,  MELTING  PRODUCTS,  ETC.,  WHICH 
ARE  NOT  ALLOYS. 

1.  Assays  for  Rich  Silver  Ores. 

a.  Melting  with  Metallic  Lead  ( Scorification )  and  Cupella- 
tion of  Lead. — One  hundred  parts  of  the  sample,  contain- 
ing sulphur,  antimony,  arsenic,  and  earths  are  mixed 
with  four  hundred  parts  of  test  lead  in  a  scorifier  (clay 
vessel)  and  covered  with  four  hundred  parts  more  of 
lead.  This  proportion  of  lead  and  ore,  eight  to  one,  is 
generally  sufficient,  but  if  there  is  a  considerable  quan- 
tity of  zincblend  in  the  ore,  twelve  to  fourteen,  and  in 
presence  of  much  copper  or  tin,  twenty  to  thirty  times 
13 


194  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

as  much  lead  is  required,  as  the  weight  of  the  ore.  An 
addition  0*1  or  0*16  parts  of  borax  is  necessary  then, 
when  the  ore  contains  a  great  deal  of  earthy  matter  or 
zincblend.  The  charged  scorifier  is  introduced  into  the 
red-hot  muffle,  the  muffle  closed  and  strong  heat  applied 
for  fifteen  or  twenty  minutes.  Then  the  muffle  is 
opened  and  the  melting  continued  till  the  lead  becomes 
entirely  covered  with  lead  slag.  The  muffle  is  then 
closed  again  for  fifteen  minutes,  then  the  scorifier  taken 
out,  and  its  contents  immediately  poured  into  a  circular 
ingot  mould.  When  cold,  the  lead  button  is  hammered 
square,  the  sharp  edges  and  corners  hammered  down 
and  the  button  finally  cupelled. 

The  lead  button  is  placed  on  the  red-hot  cupel  and 
the  heat  raised.  As  soon  as  the  lead  is  perceived  to 
work,  the  muffle  is  opened  again  to  admit  the  air.  The 
cupellation  must  be  executed  at  the  lowest  possible 
heat.  The  guides  for  the  right  temperature  are  the 
rising  lead  fumes  and  the  glowing  of  the  cupel.  If  the 
fumes  rise  slowly  to  the  middle  of  the  muffle  and  the 
cupel  glows  reddish-brown,  it  indicates  the  right  tem- 
perature ;  but  if  the  fumes  disappear  immediately  above 
the  cupel,  which  appears  light  red,  the  temperature  is 
too  high.  In  this  case,  some  broken  pieces  of  crucible 
may  be  introduced  in  the  rear  of  the  cupels.  The  tem- 
perature must  be  raised  again  at  the  end  of  the  opera- 
tion. The  cupel  is  then  removed  and  the  silver  button 
weighed. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  195 

b.  Melting  of  Argentiferous  Lead  Ores  and  Melting 
Products  without  addition  of  Lead,  and  Cupellation  of  the 
Begulus. — Ores  or  other  substances  containing  sufficient 
lead,  and  not  rich  in  silver,  are  melted  like  lead  assays. 
The  obtained  lead  button  is  weighed  and  then  cupelled. 
This  method  is  applied  to  ores  containing  not  more 
than  about  fifty  ounces  of  silver  per  ton  and  not  less 
than  six  hundred  pounds  of  lead,  also  lead-matt,  hearth, 
scrapings,  litharge,  etc. 

^  c.  Melting  of  Unroasted  Ores  with  Litharge  or  Acetate  of 
Lead  and  Fluxes. — To  these  assays,  ores  are  subjected, 
not  too  rich  in  silver,  containing  sulphur,  antimony,  and 
arsenic.  The  oxygen  of  the  litharge  oxydizes  the  sul- 
phurets,  while  the  disengaged  lead  combines  with  the 
silver.  Another  part  of  the  litharge  serves  as  a  flux, 
and  dissolves  the  earthy  matters.  To  obtain  a  better 
fluxing,  other  fluxes  must  be  added,  as :  borax,  glass, 
soda,  or  potash.  The  addition  of  coal  dust,  flour,  or 
black  flux  reduces  more  lead  and  favors  the  desilveriza- 
tion  of  the  ore.  One  part  of  ore  is  mixed  with  from 
four  to  eight  parts  of  litharge,  two  parts  potash  or  soda 
and  some  calcined  borax,  also  0*06  charcoal  dust.  This 
mixture  is  placed  in  a  crucible,  covered  with  salt  and 
melted.  The  heat  must  be  kept  moderate,  till  the 
mixture  is  melted  down.  The  temperature  is  then 
raised  nearly  to  white  heat  for  about  fifteen  minutes, 
whereupon  the  crucible  is  taken  out,  and  when  cold 
broken.  This  method  is  not  quite  so  perfect  as  the 
scorification,  a. 


196  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

d.  Melting  of  Roasted  Silver  Ore  with  Litharge  and 
Black  Flux. — This  method  yields  always  less  silver  than 
the  preceding  assays,  on  account  of  the  loss  of  silver  in 
roasting. 

2.  Assays  for  Poor  Silver  Ores. 

Generally,  the  assays  for  rich,  are  adapted  also  for 
the  poor  ores.  The  procedure  differs  only  in  this  that  a 
little  larger  quantity  is  weighed  out,  and  that  several 
assays  are  made  of  one  sample,  the  lead  buttons  of 
which  are  cupelled  into  one  silver  grain. 

a.  Ores  rich  in  Sulphurets,  Arsenical  or  Antimonial  Com- 
binations.— For  instance,  iron  pyrites,  arsenical  pyrites, 
blends,  etc.,  are  best  melted  with  litharge  in  crucibles 
1  c.  The  scorification  is  less  suitable,  unless  the  test 
lead  is  quite  free  from  silver.  Yery  poor  galena  may 
be  melted  with  thirty  or  forty  per  cent,  of  saltpetre 
and  one  hundred  per  cent,  of  soda,  or  better  one  hun- 
dred per  cent,  of  litharge.  Also  one  ounce  galena  with 
one  and  a  half  ounces  black  flux,  0*1  ounce  iron  filings, 
and  five  ounces  of  soda,  or  with  0'5  ounces  saltpetre, 
7*5  litharge,  and  five  ounces  of  soda. 

b.  Ores  containing  a  great  quantity  of  Earths. — For 
instance,  very  poor  tailings,  slag,  etc.,  are  assayed  in 
the  following  manner :  Half  ounces  of  the  sample  are 
weighed  out  from  six  to  eight  times  and  each  separately 
mixed  with  1*5  or  two  ounces  of  soda  and  O05  charcoal 
dust,  then  introduced  in  so  many  crucibles,  each  covered 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  197 

with  half  an  ounce  granulated  test  lead,  and  finally  with 
salt.  The  crucibles  are  then  exposed  to  one  or  one  and 
a  half  hours'  moderate  melting,  after  which  a  strong 
heat  is  applied  for  fifteen  minutes  more,  and  the  assays 
taken  out.  The  six  or  eight  lead  buttons  obtained  by 
this  melting  are  laid  in  scorifiers  under  the  muffle,  and 
by  oxydizing  concentrated  into  one  button,  which  is 
then  cupelled.  At  the  same  time,  six  or  eight  ounces  of 
the  same  test  lead  must  be  concentrated  and  cupelled 
and  the  amount  of  silver  obtained  subtracted  from  the 
assay.  It  may  be  necessary  to  concentrate  ten  or 
more  assays  into  one  when  the  ore  is  very  poor.  An 
assay  of  slag  can  be  melted  with  nine  hundred  per  cent, 
of  litharge  and  08  per  cent,  of  quartz  without  other 
fluxes. 

H.   PROCEEDING  FOR  ARGENTIFEROUS  ALLOYS. 

Argentiferous  lead,  pig  lead,  and  bismuth  are  sub- 
jected directly  to  cupellation  in  quantities  of  one-half 
or  one  ounce.  If  poor  in  silver,  several  ounces  may  be 
concentrated  by  scorification  before  being  cupelled. 

Argentiferous  tin  and  zinc  must  be  first  oxydized 
under  the  muffle,  then  scorified  with  sixteen  parts  of 
test  lead  and  four  parts  of  borax,  or  they  may  be  melted 
in  a  crucible  with  litharge  and  black  flux. 

Argentiferous  wrought-iron,  cast-iron,  or  steel  are  first 
oxydized  by  means  of  nitric  acid,  then  the  dried  oxyd 
scorified  with  eight  to  twelve  parts  lead,  two  or  three 
of  borax  and  one  of  powdered  glass.  The  lead  is  sub- 
jected to  cupellation. 


198  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Argentiferous  copper,  black  copper,  brass,  etc.,  are 
first  broken  in  small  pieces,  tben  one-fourth  of  an  ounce 
of  either  scorified  with  sixteen  to  thirty  parts  of  test 
lead,  and  then  cupelled. 

Cupriferous  Silver. — Before  a  proper  cupellation  can  be 
carried  out,  it  is  necessary  to  know  the  aproximative 
alloy  of  copper.  For  this  purpose  the  test  is  first 
cupelled  with  ten  or  fifteen  parts  of  lead,  and  the 
quantity  of  copper  ascertained.  Pure  silver  should  be 
cupelled  with  03  of  its  weight  of  lead ;  an  alloy  of 
fifteen  silver  and  one  copper  requires  three  times  as 
much  lead ;  fourteen  silver  and  two  copper  should  be 
cupelled  with  seven  fold ;  twelve  silver  and  four  copper 
with  ten  fold ;  eleven  silver  and  five  copper  with  twelve 
fold ;  nine  silver  and  seven  copper  with  fourteen  fold, 
and  eight  to  one  silver  and  eight  to  fifteen  copper  with 
sixteen  or  seventeen  fold  quantity  of  lead. 

The  cupel  absorbs  about  as  much  litharge  as  its  own 
weight,  whereby  the  size  of  the  cupel  is  indicated  for 
a  certain  quantity  of  lead.  The  copperous  silver  is 
wrapped  in  a  piece  of  paper  or  lead-foil  and  introduced 
into  the  glowing  cupel,  then  the  lead  in  one  piece,  or 
the  lead  may  be  first  brought  into  the  cupel,  and  then, 
when  it  becomes  bright,  the  alloy  added.  As  soon  as 
the  test  commences  to  work  at  a  strong  heat,  the  tem- 
perature must  be  diminished,  and  only  at  the  end  of  the 
operation  increased.  The  regulation  of  the  temperature 
is  effected  by  closing  or  opening  the  draft  holes. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  199 


B.   WET  ASSAYS. 

Sec.  63.  This  method  (Gay-Lussac's)  is  very  suitable 
for  rich  alloys  and  gives  the  most  accurate  results.  A 
determined  weight  of  silver  is  dissolved  in  nitric  acid, 
and  precipitated  by  a  graduated  solution  of  common 
salt.  The  calculation  is  then  made  on  the  quantity  of 
the  solution  used  for  the  precipitation.  One  hundred 
cubic  centimetres  of  the  standard  salt  solution  precipi- 
tate one  gramme  of  silver. 


C.    BLOWPIPE  ASSAYS. 

t.  Argentiferous   Ores   and   Substances   which  are  not 

Alloys. 

Sec.  64.  The  fine  pulverized  test  is  mixed  with  fine- 
sifted  lead  (free  from  silver)  and  with  borax  glass,  then 
melted,  and  the  lead  cupelled.  This  assay  consists  of 
the  following  operations : 

a.  The  Dressing  of  the  Assay. — The  required  quantity 
of  borax-glass  depends  on  the  fusibility  of  the  sub- 
stance. For  assays  that  fuse  with  difficulty,  for  instance, 
iron  or  arsenical-pyrites,  nickel  or  cobalt  ores,  one  grain 
of  borax  is  sufficient  for  one  grain  of  ore.  The  quantity 
of  lead  depends  on  the  quantity  of  substances  which  are 
difficult  to  scorify,  for  instance  copper,  but  especially 
nickel  and  cobalt.    If  there  is  not  over  seven  per  cent. 


200  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

of  copper  or  ten  per  cent,  of  nickel,  five  grains  of  lead 
to  one  grain  of  ore  will  answer.  Ten  or  twelve  per 
cent,  of  copper  (bournonit,  eucairit,  tin  pyrites)  require 
seven  grains  of  lead.  Thirty  to  fifty  per  cent,  of  copper 
(silver-copper  glance,  copper  pyrites,  copper  blend,  fah- 
lerz,  tenantit  or  copper  matt)  must  be  mixed  with  ten 
grains  of  lead.  Sixty-five-seventy  per  cent,  of  copper 
(purple  copper)  require  twelve  grains  and  eighty  per 
cent,  of  copper  (copper  glance)  fifteen  grains  of  test 
lead. 

Silver  sulphurets,  roasted  lead,  and  silver  ores,  amal- 
gamation and  extraction  tailings,  brornic,  iodic,  chloro- 
bromic  silver,  hearth,  argentiferous  slag,  etc.,  are  dressed 
with  five  grains  of  lead  0*5  grains  of  borax-glass  and 
the  obtained  lead  button  cupelled.. 

The  weighed  ore  and  fluxes  are  mixed  in  the  capsule 
with  the  handle  of  the  little  spoon,  and  by  means  of  a 
hair  brush  or  spatula  introduced  into  a  soda-paper  tube, 
closed  at  one  end.  The  open  end  is  folded  and  the  tube 
placed  in  a  cylindrical  hole  in  a  piece  of  charcoal,  made 
with  a  coal  borer. 

b.  The  Fusion. — The  paper  is  first  burnt  off  with  a 
feeble  flanve,  then  the  whole  test  covered  with  a  strong 
reduction  flame,  which  must  continue  till  slag  and  lead 
appear  separated.  The  slag  must  be  free  of  lead 
globules.  Under  these  circumstances  all  the  silver  is 
taken  up  by  the  lead,  and  the  earthy  matters  by  the 
borax.    The  fusion  is  now  finished.    But  it  is  generally 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  201 

the  case  that  different  volatile  substances  are  combined 
with  the  lead  ;  for  instance,  sulphur,  antimony,  etc., 
which  must  be  driven  out  by  longer  blowing  with  the 
oxydation  flame,  directed  on  the  lead  button.  This 
operation  must  continue  till  the  lead  appears  white 
when  cold.  It  is  then  taken  out  with  steel  forceps  and 
freed  from  adhering  slag  on  the  steel  anvil,  giving  it  a 
cubic  shape. 

c.  First  Cupelling. — The  cupel  is  prepared  from  sifted 
boneash,  which  is  beaten  in  a  little  iron  mould  by  gently 
striking  the  pestle  with  the  hammer.  This  iron  mould 
is  placed  on  a  small  wooden  stand  and  glowed  with  the 
flame.  When  this  is  done,  the  lead  button  is  laid  on  the 
cupel  and  melted  with  the  blue  flame,  which  must  touch 
the  lead  till  it  begins  to  operate.  The  blue,  sharp  point- 
ed flame  is  then  kept  a  little  further  off,  being  always 
directed  on  the  button,  which  must  be  kept  at  a  mod- 
erate red  heat,  so  that  the  rising  litharge  may  congeal 
on  the  sides.  If  the  heat  is  too  strong,  the  lead  evapo- 
rates, and  the  litharge  draws  into  the  cupel-mass,  or  fuses 
over  the  test.  If,  on  the  other  hand,  the  temperature  is 
too  low,  the  litharge  accumulates  too  much  on  the  lead, 
covering  the  latter,  and  stopping  the  operation.  When 
the  lead  button  is  reduced  to  the  size  of  a  hemp  seed, 
the  blowing  must  be  stopped,  the  button  seized  with  a 
pair  of  pincers,  freed  from  boneash  and  flattened  some- 
what. 

d.  Fine  Cupelling. — The  used  boneash  is  removed  from 


202  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  iron  mould,  and  another  test  beaten  in,  with  a  smooth 
surface,  which  is  best  obtained,  if  levigated  boneash  is 
mixed  with  the  sifted.  After  the  cupel  has  been  dried 
by  the  oxydation  flame,  the  flattened  lead  is  placed  on 
the  side  of  the  test  and  exposed  to  the  oxydation  flame. 
In  melting,  it  assumes  the  globular  form.  The  cupel 
must  be  held  inclined,  and  slowly  turned,  so  that  the 
button  can  slide  on  the  surface  of  the  test.  The  flame  is 
directed  always  around  the  lead,  and  so  much  heat 
applied,  that  the  button  appears  red-hot  and  the  litharge 
disappears  in  the  cupel-mass.  When  the  button  assumes 
the  greenish  color  of  fused  silver,  the  operation  is  fin- 
ished. 

e.  The  Weighing. — The  weight  of  the  silver  globule  is 
determined  either  by  weighing  on  the  balance  with 
gramme  or  grain  weights,  or,  if  too  small,  by  measuring 
it  on  a  scale.  The  scale  is  engraved  on  polished  ivory. 
There  are  two  convergent  lines  forming  an  acute  angle. 
These  lines  are  divided  into  equal  sections  by  parallel 
lines,  crossing  the  convergent  lines.  On  the  right  side, 
each  section  shows  the  per  centage  of  silver.  The  round 
or  spherical  silver  globule  is  placed  between  the  conver- 
gent lines  and  moved  down,  till  it  becomes  tangented  by 
the  convergent  lines.  The  numbers  on  the  right  side 
show  then  the  amount  of  silver.  This  measuring  must  be 
done  with  the  aid  of  the  magnifying  glass. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  203 

2.  Argentiferous  Alloys. 

Alloys  rich  in  silver,  for  instance,  native  silver,  amal- 
gam silver,  silver  coin,  etc.,  are  dressed  with  one  grain  of 
test  lead,  and  twenty-five  per  cent,  of  borax  glass  to  one 
grain  of  alloy.  Alloys  containing  more  copper  must  be 
fused  with  from  two  to  five  grains  of  lead.  This  is  done 
in  a  groove  on  the  charcoal  with  the  reduction  flame,  till 
lead  and  alloy  are  melted  into  one  mass  and  no  globules 
are  perceived  in  the  slag.  It  is  then  cupelled  and 
weighed. 

Poor  substances  can  be  cupelled  directly,  if  suitable 
for  cupellation,  for  instance,  pig  lead,  or  argentiferous 
bismuth.  Of  these  substances,  two  to  five  grains  may 
be  weighed  out  for  cupellation.  Copper  and  nickel  con- 
taining alloys  (block  copper,  German  silver,  brass,  cop- 
per coin)  must  be  weighed  out  in  portions  of  one-half 
grains,  and  fused  with  ten  grains  of  lead  and  one-half 
grain  of  borax  glass,  in  a  soda  paper  tube,  with  the 
reduction  flame.  The  obtained  button  is  cupelled.  In 
the  second,  or  fine  cupellation,  some  lead  may  be  added, 
if  a  great  deal  of  copper  is  in  the  alloy.  If  there  is  also 
tin  besides  the  copper  in  the  composition,  one  grain  of  it 
must  be  fused  with  five  to  fifteen  grains  of  lead,  one-half 
grain  of  borax,  and  one-half  grain  of  soda,  in  the  reduc- 
tion flame,  finishing  the  operation  with  the  oxydation 
flame.  If  the  lead  does  not  exhibit  a  whitish  color,  it 
may  be  melted  for  a  while  with  the  oxydation  flame  on 
another  spot  of  the  charcoal  with  borax,  and  then 


204  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


cupelled.  Argentiferous  quicksilver  combinations  are 
treated  first  in  a  closed  glass  tube  with  the  alcohol 
flame,  in  order  to  drive  off  the  quicksilver,  then  melt- 
ing the  residue  of  the  one  grain  test,  according  to  the 
amount  of  copper,  with  one  to  three  grains  of  lead  and 
some  borax.  If  the  residue  adheres  closely  to  the 
glass,  it  may  be  fused  with  the  cut  part  of  the  tube, 
lead,  and  soda.  Argentiferous  iron  and  steel  are  fused, 
one  grain  of  either,  with  one  grain  sulphur,  eight  grains 
lead,  and  one-half  grain  borax,  in  a  paper  tube.  They 
must  be  treated  with  a  good  oxydation  flame  until  all 
sulphur  is  separated,  and  the  button  shows  a  lead  color. 
A  combination  of  silver  with  tellurium,  antimony,  and 
zinc,  is  melted  with  five  grains  of  lead  and  some  borax, 
with  the  reduction,  and  finally  with  the  oxydation  flame. 


CHAPTER  II. 


METHODS  OF  EXTRACTING  SILVER 

Sec.  65.  The  extraction  of  silver  requires  generally 
complicated  processes,  as  it  occurs  in  most  cases  com- 
bined with  other  minerals  which  must  be  removed  before 
the  silver  can  be  obtained.  Generally  there  are  three 
methods  in  use  by  which  the  silver  is  extracted,  the 
choice  of  which  depends  on  the  nature  of  the  ore :  1. 
Melting  of  silver  ores  with  lead ;  2.  Amalgamation,  and 
3.  Dissolving  and  precipitating  the  silver. 

1.  In  Melting  Silver  Ores  with  Lead,  Oxyd  of  Lead,  or 
Lead  Ores — silver  containing  lead  (pig  lead)  is  produced, 
which  is  separated  directly  by  cupellation,  or  if  the  lead 
is  poor  in  silver,  the  latter  is  concentrated  in  the  lead  by 
Pattinson's  method.  The  advantage  of  this  procedure 
depends  principally  on  the  price  of  fuel  and  lead,  if  the 
latter  is  not  present  in  the  ore.  The  greatest  part  of 
the  produced  silver  is  extracted  from  argentiferous  lead 
and  copper  ores,  the  smaller  portion  of  real  silver  ores. 
The  extraction  of  silver  from  argentiferous  galena  is  one 
of  the  oldest  processes  which,  by  its  simplicity,  is  now 


206  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

conducted  almost  in  the  same  way  as  it  may  have  been 
thousands  of  years  ago.  The  extraction  of  silver  from 
argentiferous  copper  ores,  requiring  more  advanced 
metallurgical  knowledge,  is  a  later  process.  The  extrac- 
tion of  silver  may  be  executed  on  copper  ores  or  on  its 
melting  products  (copper  matt  or  black  copper),  but  this 
process  must  always  be  considered  very  imperfect,  on 
account  of  the  considerable  loss  of  silver,  lead,  and  cop- 
per. The  affinity  of  these  metals  for  each  other  makes 
the  process  complicated  and  expensive.  Copper  ores  not 
rich  in  silver  are  subjected  to  melting  by  which  the  sil- 
ver is  concentrated  in  the  obtained  black  copper,  this 
being  separated  from  silver  by  liquation.  Copper  ores 
rich  in  silver  are  melted  with  lead  or  lead  ores,  by  which 
a  suitable  copper  is  obtained  for  the  liquation.  To  avoid 
this  liquation  process,  repeated  roasting  and  melting  of 
copper  matt  with  lead  containing  substances  is  adopted, 
but  the  desilverization  of  the  matt  is  imperfect. 

Although  the  behavior  of  silver,  copper,  and  lead 
towards  the  sulphur,  on  which  this  process  is  principally 
based,  is  well  understood,  the  imperfections  are  not  yet 
removed.  For  this  reason  more  attention  is  now  paid  to 
the  working  of  argentiferous  copper  ores  by  amalgama- 
tion and  precipitation  processes. 

It  is  preferable  to  add  rich  silver  ores  to  the  lead  in 
the  cupelling  furnace,  poor  silver  ores  bare  of  such  sub- 
stances as  collect  the  silver  from  the  slag,  are  fused  with 
iron  pyrites,  if  no  lead  ore  can  be  obtained.  The  earthy 
substances  scorify  and  the  silver  is  taken  up  by  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  207 

sulphide  of  iron  (iron  matt)  which  must  be  treated 
afterwards  with  lead.  Most  of  the  silver  ores  are  cop- 
periferous  to  some  degree,  yielding,  also,  copperiferous 
matt,  of  which  the  silver,  by  means  of  lead,  cannot  be 
extracted  perfectly.  The  copper  makes  the  process  com- 
plicated. In  melting,  the  scorification  of  the  silver  is 
prevented  by  the  great  affinity  of  sulphur  to  silver. 

According  to  Karsten,  poor  copperiferous  silver  ores 
can  be  worked  advantageously  for  silver,  under  favora- 
ble circumstances,  when  the  ore  contains  only  ten  ounces 
of  silver  to  the  ton.  But  also  six  and  even  three  ounces 
per  ton  will  pay  the  extraction,  if  copper  or  lead  is 
obtained  from  the  same  ore.  The  value  of  silver  is 
eighty  times  higher  than  that  of  copper,  and  four  hun- 
dred times  higher  than  lead. 

The  silver  containing  lead,  obtained  in  either  way,  is 
parted  by  an  oxydation  process  more  than  a  thousand 
years  old,  called  cupellation.  If  the  lead  is  poor  in  sil- 
ver, it  is  first  subjected  to  the  Pattinson's  crystallization 
process,  by  which  the  silver  is  concentrated  in  the  lead. 
Parke's  method  of  extracting  the  silver  from  the  lead  by 
zinc,  promising  great  advantages,  is  not  yet  extensively 
practiced,  on  account  of  some  of  the  zinc  remaining  in 
the  lead. 

2.  The  Amalgamation  or  Extraction  of  Silver  by  Quicksil- 
ver in  the  Wet  Way — is  based  on  the  facility  with  which 
mercury  unites  with  the  silver,  forming  amalgam.  It  is 
easily  separated  by  glowing.    This  process  is  said  to 


208  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

have  been  discovered  about  the  middle  of  the  sixteenth 
century  in  Mexico,  and  became  known  in  Europe  in  the 
latter  part  of  the  seventeenth  century. 

This  process  is  preferable  to  the  preceding,  when  fuel 
is  expensive,  or  in  treating  poor  silver  ores,  argentifer- 
ous copper  ores,  or  copperous  products,  free  of  lead.  Of 
poor,  earthy  silver  ores,  the  silver  can  be  concentrated 
in  sulphide  of  iron  (iron  matt)  by  melting  with  iron 
pyrites.  Only  the  real  silver  ores  are  subjected  directly 
to  amalgamation.  From  argentiferous  copper  ores  the 
silver  is  concentrated  in  the  copper  matt,  or  in  black 
copper ;  these  products  are  then  amalgamated,  allowing 
thus  a  cheaper  manipulation,  a  more  perfect  silver 
extraction,  less  loss  in  copper,  and  the  production  of 
.purer  copper,  than  the  melting  process.  The  European 
amalgamation  has  the  advantage  over  the  American 
(patio)  in  yielding  more  silver,  there  being  considerably 
smaller  loss  in  quicksilver,  while  the  patio  amalgamation, 
on  the  other  hand,  can  be  carried  on  without  buildings 
and  fuel. 

3.  Solution  and  Precipitation  of  Silver. — There  are  prin- 
cipally two  processes,  lately  invented  by  Augustin  and 
Ziervogel,  which  are  superior  to  amalgamation,  being 
simple,  cheap,  and  extracting  the  silver  in  a  short  time. 
Augustin  transforms  the  silver  into  a  chloride,  by  a  chlo- 
ridizing  roasting,  dissolves  the  chloride  in  concentrated 
solution  of  common  salt,  and  precipitates  the  silver 
by  copper.    Ziervogel  roasts  the  ore,  under  conditions 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  209 

that  the  silver  is  converted  into  a  sulphate,  which  is  sol- 
uble in  hot  water  and  can  be  precipitated  by  copper, 
after  lixiviation.  This  last  method  is  more  simple,  but 
leaves  richer  tailings  than  the  preceding.  Both  processes 
give,  then,  only  a  good  result,  if  the  roasting  is  conducted 
with  the  utmost  care,  and  if  the  ore  or  matt  is  free  from 
lead,  zinc,  antimony,  and  arsenic,  or,  at  least,  if  only 
small  quantities  of  these  injurious  metals  are  present. 
The  use  of  these  two  processes,  therefore,  is  limited  to 
places  where  pure  ore  is  found,  or  pure  matt  obtained. 

Other  extracting  methods  of  this  class,  for  instance, 
by  common  salt  and  ammoniac,  salt  and  chloride  of  cop- 
per, etc.,  have  to  be  considered  as  experiments  rather 
than  established  processes. 

According  to  the  preceding,  the  most  suitable  way  of 
treating  the  following  different  silver  ores  will  be : 

1.  Real  Silver  Ores — With  earthy  and  sulphuretted  sub- 
stances, with  pyrites,  blend,  and  copperous  ores,  must  be 
treated  according  to  their  richness : 

a.  Rich  or  middling  rich  ores  containing  fifty  to  ninety 
per  cent,  of  silver,  are  best  subjected  directly  to  cupella- 
tion  with  lead.  Forty  per  cent,  or  less  silver  containing 
ores  can  be  melted  with  lead  ores  and  fluxes  in  a  vertical 
blast  furnace.  Such  ore  cannot  be  worked  to  advantage 
by  amalgamation  (except  in  pans,  as  already  described). 
Very  rich  ores,  especially  if  they  contain  native  silver, 
are  melted  also  in  crucibles  with  proper  fluxes. 

14 


210  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

b.  Poor  ores  of  this  class,  containing  from  two  and  a 
half  to  forty  ounces  per  ton,  are  subjected  to  melting 
with  iron  pyrites  (melting  for  matt).  The  silver  of  the 
obtained  matt  can  be  extracted  either  by  lead  or  by 
quicksilver.  The  extraction  with  lead  is  proportionately 
more  perfect  the  less  quantity  of  copper  there  is  in  the 
matt.  Ore  with  from  forty  to  sixty  ounces  of  silver  per 
ton  can  be  amalgamated  with  a  proper  addition  of  iron 
pyrites  in  roasting. 

2.  Pyritous  ores,  containing  silver  ores  disseminated 
in  iron  pyrites,  yielding  sufficient  matt  in  melting,  are 
subjected  to  such  melting  in  blast  furnaces,  and  the 
obtained  matt  treated  with  quicksilver  or  lead.  Eicher 
in  silver,  this  class  of  ore  is  best  suited  for  the  amalga- 
mation, but  the  presence  of  copper  pyrites,  arsenical 
pyrites,  zinc  blend,  or  galena,  is  not  favorable.  Eicher 
ore  may  be  also  melted  with  lead  containing  ores  after 
roasting. 

3.  Argentiferous  lead  ores  are  entirely  unsuitable  for 
amalgamation.  Their  beneficiation  is  best  effected  by 
melting,  and  it  depends,  further,  on  the  choice  of  the 
most  suitable  desilverization  of  the  different  products. 
The  less  copper  in  the  ore,  the  easier  and  more  perfect 
the  extraction  of  silver  and  lead. 

4.  Argentiferous  copper  ores  can  be  treated  in  differ- 
ent ways : 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  211 

a.  The  poorer  ore  is  subjected  to  melting  for  matt,  or 
black  copper.  From  these  products,  the  silver  is  then 
extracted.  The  copper  matt  is  desilvered  either  by  lead 
or  quicksilver,  or  by  Augustin's  or  Ziervogel's  methods. 
Argentiferous  black  copper  is  oftener  treated  with  lead 
than  with  quicksilver.  The  direct  amalgamation  of  argen- 
tiferous copper  ores  is  often  disadvantageous. 

b.  Richer  copper  ores  are  melted  with  proper  dressing 
in  roasted  or  unroasted  condition,  with  roasted  or  un- 
roasted  lead  ores. 

c.  Very  poor  copper  ores  are  added  to  the  melting 
for  iron  matt  (melting  with  iron  pyrites). 

5.  Argentiferous  blend  and  arsenical  pyrites  must  be 
roasted,  then  subjected  to  melting  for  iron  matt.  In 
roasting  such  ores,  a  considerable  loss  of  silver  may 
occur.  If  melted  without  roasting,  the  blend  causes  a 
matt  fusible  with  difficulty,  by  which  the  silver  is  not 
perfectly  collected.  Argentiferous  arsenic  can  be  melted 
with  lead  after  careful  roasting. 

6.  Argentiferous  cobalt  ores  are  beneficiated,  first  for 
smalt,  the  silver,  then  extracted  from  the  residue  by 
lead  or  amalgamation. 

Sec.  66.  The  principal  known  methods  of  extracting 
silver  can  be  brought  into  the  following  division : 


212  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

EXTRACTION  OF   SILVER  IN  THE   DRY  WAY. 

A.    Lead  Manipulation  with  Argentiferous  Ores. 

a.  Melting  of  rich  silver  ores  in  crucibles  with  lead  or 
litharge. 

b.  Fusion  of  rich  silver  ores  with  lead.  (Cupellation.) 

c.  Melting  of  rich  unroasted  silver  ores,  with  roasted 
or  unroasted  lead  ores,  or  plumbiferous  products,  cast 
iron,  lime,  or  iron  slag  (virtuous  slag)  in  blast  furnaces. 

d.  Melting  of  argentiferous  lead  glance  in  unroasted 
condition,  with  desulphurating  substances  (metallic  iron, 
iron  ore,  ferriferous  matts,  etc.). 

e.  Melting  of  roasted  argentiferous  lead  glance  with 
desulphurating  substances  (cast  iron,  roasted  iron  matt, 
and  iron  slag). 

/.  Melting  of  pure  unroasted  lead  ores  without  desul- 
phurating agents.  (Melting  in  North- American  lead 
hearths). 

g.  Melting  of  roasted  argentiferous  lead  ores  without 
desulphurating  agents  in  blast  furnaces,  in  reverberatory 
furnaces,  or  in  hearth  furnaces. 

h.  Melting  of  roasted  argentiferous  copper  ores  with 
roasted  lead  ores,  or  with  products  of  cupellation. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  213 

B.    Lead  Manipulation  with  Argentiferous  Matts 

Which  are  obtained,  either  in  melting  of  argentifer- 
ous ores  with  iron  pyrites,  or  in  melting  of  argentiferous 
lead  and  copper  ores  : 

a.  Treatment  of  the  unroasted  iron,  or  copper  matt 
with  metallic  lead : 

1.  Fusion.  The  melted  matt  is  mixed  with  melted 
lead. 

2.  Hydrostatic  Melting.  The  melted  matt  is  forced 
through  a  body  of  fused  lead. 

b.  Melting  of  unroasted  copper  matt  with  plumbifer- 
ous  products. 

c.  Melting  of  roasted  iron  matt  with  roasted  or 
unroasted  lead  ores  or  with  products  of  cupellation. 

d.  Melting  of  unroasted  lead  matt  with  unroasted 
galena  and  iron. 

e.  Melting  of  roasted  lead  matt  with  iron. 

/.  Melting  of  roasted  lead  matt  without  desulphurating 
agents. 

C.  Melting   Lead  with  Argentiferous  Black  Copper 
(Liquation.) 

D.    Extraction  of  Silver  with  Copper  and  Lead. 

Argentiferous  copper  matt  is  melted  with  black  cop- 
per, spongy  copper  from  liquation,  and  plumbiferous  pro- 


214  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

ducts,  whereby  a  part  of  the  silver  is  disengaged  by  the 
copper  and  taken  up  by  the  lead. 

E.    Separation  of  Silver  from  Argentiferous  Lead. 

a.  Cupelling  in  furnaces  with  a  fixed  hearth. 

b.  Cupelling  in  furnaces  with  a  movable  hearth. 

F.    Concentration  of  Silver  in  Pig  Lead  by  Pattinson's 
Crystallization  Process. 

G.    Refining  of  Silver"obtained  from  Cupellation. 

a,  Kefining  in  ovens  with  fixed  or  movable  tests  : 

1.  Under  the  muffle. 

2.  Before  the  bellows. 

3.  In  reverberatory  furnaces  with  movable  or  immov- 
able tests. 

b.  Refining  in  crucibles  with  or  without  agents. 

H.    Desilverization  of  Lead  by  Zinc. 

EXTRACTION  OF  SILVER  IN  THE  WET  WAY. 

A.    Extraction  by  Quicksilver.  (Amalgamation). 

a.  European  barrel  amalgamation. 

b.  Amalgamation  of  ores. 

c.  Amalgamation  of  copper  matt. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  215 

d.  Amalgamation  of  speiss  (arsenides,  ger.  speise). 

e.  Amalgamation  of  black  copper. 

/.  American  heap  amalgamation.  (Patio.) 

g.  Combined  American  and  European  amalgamation. 

B.  Extraction  by  Solution  and  Precipitation.  (Augustin's 

Method). 

a.  Extraction  of  silver  from  matts. 

b.  Extraction  of  silver  from  ores. 

c.  Extraction  of  silver  from  speiss  (ger.  speise). 

d.  Extraction  of  silver  from  black  copper. 

C.  Ziervogel's  Water  Lixiviation  on  Argentiferous  Cop- 

per Matt. 


D.    Patera's  Method  op  Extraction  of  Silver  from  Ores. 


CHAPTER  III. 


EXTRACTION  OF  SILVER  IN  THE  DRY  WAY. 

Extraction  of  Silver  with  Lead. 

Sec.  67.  The  use  of  lead  for  the  extraction  of  silver  is 
based : 

1.  On  the  property  of  the  lead  to  decompose  the  sul- 
phide of  silver  under  formation  of  sulphide  of  lead.  If 
there  are  other  sulphuretted  metals  in  the  silver  ore, 
especially  iron  and  copper  sulphurets,  they  will  be  less 
decomposed  by  the  lead. 

The  products  of  melting  are  argentiferous  lead  and 
matt  of  iron,  copper,  and  lead.  The  less  copper  there 
is  in  the  ore,  the  easier  and  more  perfect  the  extrac- 
tion of  silver,  because  the  sulphide  of  copper  retains 
a  part  of  the  sulphide  of  silver  in  the  matt  with  great 
obstinacy,  and  causes  a  repetition  of  the  extraction.  The 
silver  ores  are  very  seldom  free  of  argentiferous  copper 
ores ;  a  copperous  matt  is  therefore  always  obtained,  the 
silver  of  which  never  can  be  extracted  perfectly  by  lead 
or  lead  ores.  This  portion  of  the  silver  is  therefore 
given  up  entirely,  or  extracted  by  liquation,  when  black 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  217 

copper  is  obtained  from  the  matt.  The  sulphides  of 
iron  and  lead  also  retain  a  small  amount  of  silver. 

This  chemical  process  takes  place  in  melting  rich 
silver  ore  with  lead  crucibles,  with  lead  in  a  cupelling 
furnace  or  in  treating  argentiferous  matt  with  metallic 
lead,  also  partly  in  melting  argentiferous  lead  glance 
with  metallic  iron. 

2.  On  the  decomposing  action  of  oxyd  of  lead  and  of 
sulphate  of  lead  on  sulphuret  of  silver  in  such  a  way 
that  argentiferous  lead  and  sulphurous  acid  are  formed. 
This  process  occurs  if  unroasted  sulphuretted  silver  ores 
or  argentiferous  matts  are  melted  with  roasted  lead 
ores  or  oxydized  lead  combinations.  The  reduced  lead 
acts  also  on  the  sulphide  of  silver  in  the  manner  men- 
tioned under  1.  In  this  mode  of  melting  also  the 
appearance  of  matt  with  some  silver  cannot  be  avoided, 
inasmuch  as  some  of  the  undecomposed  roasted  lead 
ore  and  the  sulphides,  contained  in  the  silver  ore,  also 
the  sulphides  of  reduced  sulphates  form  argentiferous 
matt. 

3.  On  the  reductive  action  of  lead  on  oxyd  of  silver  or 
on  sulphate  of  silver.  This  reaction  takes  place  in  cases 
mentioned  under  1  and  2,  if  roasted  silver  ores  or  matts 
come  in  contact  with  lead.  Sulphuret  of  silver,  roast- 
ed by  itself  can  be  transformed  perfectly  into  metallic 
silver,  emitting  sulphurous  acid,  but  combined  with 
other  sulphurets,  for  instance  with  sulphurets  of  iron  or 
copper,  a  part  of  sulphate  of  silver  is  always  formed, 


218  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

which  decomposes  at  a  higher  temperature  than  the 
sulphates  of  iron  and  copper. 

4.  On  the  greater  affinity  of  silver  for  lead,  than 
copper.  A  fusion  of  argentiferous  copper  and  lead 
produces  a  compound  of  argentiferous  lead  and  a  more 
difficultly  fusible  alloy  of  about  three  parts  copper  and 
one  part  of  lead  with  a  small  amount  of  silver.  The 
argentiferous  lead  can  be  separated  from  the  copper  by 
liquation. 

The  extraction  of  silver  with  lead  is  an  imperfect 
process,  it  suffers  a  great  loss  in  silver,  copper,  and  lead, 
is  complicated  and  expensive  and  furnishes  a  copper  of 
low  quality.  In  place  of  this  mode  the  more  perfect 
amalgamation  process  is  adopted,  which  again  com- 
mences to  give  way  to  the  still  simpler  and  cheaper 
silver  extracting  processes  of  Augustin  and  Ziervogel. 
The  choice  of  beneflciating  methods  does  not  depend  on 
the  nature  of  the  ore  alone,  but  also  on  the  local  circum- 
stances, for  instance,  cheap  lead  ores,  etc.  Whether  the 
desilverization  must  be  adopted  directly  with  the  ore, 
or  with  the  matt  or  black  copper,  resulting  from  the 
ore,  depends  chiefly  on  the  amount  of  silver  and  local 
circumstances,  also  from  the  quantity  and  price  of  the 
lead  ores. 

The  loss  of  lead  in  melting  plumbiferous  ores  arises 
principally  by  scorification  and  volatilization.  The  scori- 
fication  is  produced  either  by  a  chemical  combination 
of  oxyd  of  lead  with  the  compounds  of  the  slag,  or  in  a 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  219 

mechanical  way  by  the  adhering  of  lead  or  matt  to  the 
slag.  The  remedy  for  the  first  scorification  can  be 
obtained  only  by  a  proper  dressing  of  the  ore,  for  the 
latter  principally,  by  giving  a  greater  depth  to  the 
furnace  from  the  breast  wall  to  the  back  wall.  In  this 
case  the  slag  is  bound  to  take  a  longer  time  in  flow- 
ing out,  thus  having  more  chance  to  deposit  the  lead 
globules. 

The  volatilization  of  lead  depends  on  the  speed  of  the 
blast,  which  rises  in  the  melting  room  of  the  furnace, 
and  on  the  pressure  of  the  heated  gases.  The  more 
violent  the  wind  presses  upwards  the  more  the  lead 
volatilizes.  This  occurs  mostly  near  the  nose  (slag 
channel)  at  the  back  wall,  where  the  ore  is  impregnated 
with  finely-parted  metallic  lead.  In  making  the  furnace 
deeper  from  the  breast  wall  towards  the  back  wall  in 
the  direction  of  the  wind,  contracting  the  space  above 
the  melting  region  and  giving  the  furnace  a  sufficient 
height,  the  loss  of  lead  by  volatilization  will  be  dimin- 
ished. The  height  and  depth  of  the  furnace  depends 
on  the  quantity  and  pressure  of  the  wind  required  for 
the  melting.  The  furnace  must  be  deeper  and  higher, 
if  more  wind  and  pressure  are  necessary.  The  best 
remedies  to  diminish  the  loss  of  lead  therefore,  are :  the 
height  of  the  furnace,  the  enlargement  of  the  melting 
room  in  the  direction  of  the  wind,  and  the  contraction 
above  the  tuyere. 


220  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


PRODUCTION  OF  ARGENTIFEROUS  LEAD. 

Lead  Manipulation  with  Argentiferous  Silver  Ores. 

Sec.  68.  To  this  treatment  are  subjected  rich  real 
silver  ores,  rich  roasted  pyritous  ores,  argentiferous- 
lead  and  copper  ores  in  roasted  and  unroasted  condi- 
tion, etc.  As  plumbiferous  substances  are  used :  metallic 
lead,  roasted  or  unroasted  lead  ores  and  the  products  of 
cupellation  (litharge,  heath). 

Melting  of  Rich  Silver  Ores  in  Crucibles. 

Eich  silver  ores,  are  worked  in  the  cheapest  and  most 
perfect  manner  when  added  to  cupellation.  Where  the 
cupelling  process  is  not  in  use,  the  ore  is  melted  in 
crucibles  (either  black  lead  or  clay),  generally  with  an 
addition  of  iron  to  decompose  the  sulphide  of  silver^  and 
with  some  lead  if  there  is  none  in  the  ore. 

If  the  ore  is  free  from  earthy  substances,  some  potash 
and  powdered  glass  are  added,  but  if  earths  are  present 
it  is  necessary  to  use  some  litharge,  which  forms  a 
better  slag.  The  plumbiferous-obtained  silver  is  then 
refined.  If  there  be  some  lead  and  silver  in  the  matt  it 
is  melted  again  with  an  addition  of  iron. 

The  silver  ore  from  Kongsberg,  Norway,  consists 
chiefly  of  native  silver,  silver  glance,  brittle  silver  ore, 
ruby  silver,  antimonial  silver  and  lead  glance  accompa- 
nied by  iron  pyrites,  zinc  blend,  copper  pyrites  and 
magnetic  pyrites.    The  richest  ore,  from  ten  to  thirty 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  221 

per  cent,  in  silver,  is  treated  in  crucibles.  There  is 
obtained  by  this  process  the  largest  part  of  the  Kongs- 
berg  silver  production.  The  melting  is  performed  in 
clay  crucibles  in  a  draft  furnace,  in  quantities  of  three 
hundred  pounds.  For  the  scoriflcation  of  iron  some 
quartz  and  one  per  cent,  of  borax  are  added.  The  same 
crucible  is  charged  from  four  to  six  times  daily  and  the 
following  products  obtained : 

a.  Silver  which  is  refined  on  movable  tests  of  wood 
ashes  and  lime,  with  an  addition  of  half  an  ounce  lead 
to  twenty-four  ounces  of  silver.  The  refining  of  eight 
hundred  ounces  of  silver  consumes  one  hundred  and  ten 
cubic  feet  of  pine  charcoal.  The  average  loss  of  silver 
in  refining  amounts  to  about  seventeen  per  cent. 

b.  Slag  which  is  pulverized,  the  coarser  silver  buttons 
extracted  and  the  balance  turned  over  to  the  smelting 
furnace. 

Fusion  of  rich  Silver  Ores  with  Lead  in  Cupelling  Pig 

Lead. 

When  the  lead  is  brought  so  far  in  operation  that 
litharge  commences  to  separate,  the  wind  is  stopped 
and  the  rich  ore  introduced  on  the  surface  of  the  lead 
bath  by  means  of  a  scoop,  in  quantities  of  from  one 
hundred  to  two  hundred  pounds,  according  to  the  size 
of  the  hesth.  Then  the  heat  is  raised  for  about  one 
hour.  During  the  time  the  ore  is  roasting  the  silver 
draws  into  the  lead,  the  mass  comes  into  a  very  fluid 


222  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

condition  and  the  blast  is  let  on  again.  The  slag  which 
contains  all  the  earthy  substances  of  the  ore  is  drawn 
off  with  a  wooden  pole,  and  on  account  of  some  retained 
silver  is  given  over  to  the  smelting  furnace.  To  this 
process  the  ore  is  subjected  which  contains  3,000  or 
more  ounces  of  silver  per  ton.  In  China,  roasted  ores 
are  used  for  this  method. 

Melting  of  Unroasted  Rich  Silver  Ores  with  Unroasted 
Lead  Ores  or  Plumbiferous  Products. 

This  method,  in  regard  to  silver  extraction,  is  advan- 
tageous under  circumstances.  Lead  ore  or  lead-contain- 
ing products  must  be  added  in  sufficient  quantity  to 
fully  cover  the  silver,  otherwise  a  considerable  loss  of 
silver  may  occur  by  scorification.  This  loss  increases 
if  low  furnaces  are  in  use,  and  if  the  dressed  ore  is 
hard  to  melt.  If  in  want  of  lead  ores  or  lead-containing 
products,  it  is  then  not  advisable  to  subject  too  rich 
silver  ores  to  melting  with  iron  pyrites,  concentrating 
thus  the  silver  in  the  iron  matt. 

At  Allemont  (Isere  department)  the  silver  ores  (silver 
glance  and  rubysilver)  are  dressed  in  the  following 
proportions:  one  hundred  tons  of  ore  with  about  two 
hundred  and  forty  ounces  of  silver  to  the  ton,  are 
dressed  with  one  hundred  and  fifty  tons  of  slag,  sixteen 
tons  of  quicklime,  sixteen  tons  of  iron  slag  and  as  much 
galena,  litharge,  and  hearth  as  is  necessary  to  obtain  pig 
lead,  with  about  six  hundred  and  forty  ounces  of  silver 
per  ton.    The  galena  is  decomposed  by  the  iron  of  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  223 

ore  and  by  the  iron  slag.  The  melting  is  performed 
with  charcoal  in  furnaces  three  and  a  half  feet  high. 
The  result  is  not  perfect  on  account  of  the  low  furnaces 
and  defective  dressing  of  the  ore. 

At  St.  Andreasberg,  the  furnaces  are  twenty-two  feet 
high,  and  so  much  lead  ore  is  taken  that  half  an  ounce 
of  silver  is  protected  by  seven  pounds  of  lead.  The  ore 
is  dressed :  thirty-eight  tons  of  ore,  fifty  tons  slag,  four 
to  six  tons  metallic  iron,  and  forty-eight  tons  lead- 
containing  substances.  The  obtained  pig-lead  contains 
from  one  hundred  and  sixty  to  two  hundred  and  forty 
ounces  of  silver.  The  total  loss  of  silver  in  products 
and  by  volatilization  is  from  4*43  to  4*5  per  cent. 

Melting  of  Argentiferous  Lead  Ores  in  Roasted  and 
Unroasted  condition,  generally  with  some  Argentif- 
erous Copper  Ores. 

To  this  heading  belongs  several  lead-melting  processes. 
Almost  all  galena  contains  some  silver  which  after  melt- 
ing is  found  chiefly  in  the  lead  and  partly  in  the  matt. 
The  copper  of  the  ore  concentrates  in  the  matt.  The 
silver  in  the  matt  is  in  small  quantity  and  either  not 
regarded  at  all,  or  the  roasted  matt  is  melted  either  by 
itself  or  with  plumbiferous  substances,  concentrating 
thus  the  silver  in  the  lead,  or  the  silver  is  extracted 
from  the  black  copper  obtained  from  this  matt. 


224  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Melting  of   Roasted   Argentiferous   Copper  Ores  with 
Roasted  Lead  Ores. 

This  method  is  advantageous,  if  the  copper  ores  are 
not  rich  in  silver.  If  the  amount  of  silver  is  too  large, 
it  is  exposed  to  scorification.  In  this  case,  the  ore  must 
be  melted  without  roasting  and  the  silver  collected  in 
the  matt,  which  for  the  purpose  of  desilverization  can 
be  treated  in  different  ways,  as  mentioned  further  on. 
Melting  processes,  not  melting  for  matts,  cause  a  greater 
loss  in  metals,  because  the  basis  for  scorification  in  melt- 
ing is  laid  in  the  preceding  roasting,  which  is  not  the 
case  with  unroasted  ore,  where  only  a  separation  of 
earths  and  sulphurets  takes  place. 

The  argentiferous  copper  ores  are  slightly  roasted 
and  melted  with  perfect  roasted  lead  ores  or  products 
from  cupellation  in  low  furnaces.  The  obtained  pig 
lead  must  be  cupelled.  The  matt  is  roasted  over 
several  times,  and  melted  with  the  products  of  cupella- 
tion. After  the  third  melting  with  lead  the  matt  is 
generally  free  from  silver,  but  the  matt  from  rich  ore 
usually  retains  silver  to  considerable  extent.  After 
roasting,  it  is  melted  for  black  copper  and  the  silver 
extracted  by  liquation.  This  process  is  expensive  and 
imperfect,  on  account  of  losses  in  silver,  copper  and 
lead. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  225 
| 


LEAD  MANIPULATION  WITH  ARGENTIFEROUS 
MATTS. 

Sec.  69.  Poor  silver  ores  do  not  suit  for  direct  melt- 
ing with  lead  ores.  They  produce  a  tough  melting, 
increase  the  scorification  of  lead,  etc.  Such  ores  are 
first  subjected  to  melting  for  matt,  that  is,  they  are 
melted  with  iron  pyrites.  The  earths  and  useless  oxyds 
form  the  slag,  while  the  silver  is  concentrated  in  the 
matt.  This  iron  matt,  unlike  ore,  assists  the  subse- 
quent melting  with  lead  ores,  and  protects  a  great  part 
of  the  lead  against  scorification ;  it  also  acts  as  a  pre- 
cipitation agent  for  lead  by  which  the  expense  of  the 
melting  for  matt  is  lessened.  Another  advantage  of 
this  method  is  the  beneficiation  by  the  way  of  all  rub- 
bish and  slags  of  rich  meltings  of  which  the  silver,  lead, 
and  copper  are  taken  up. 

I.    CONCENTRATION  OF  SILVER  IN  MATT. 

The  melting  for  matt  is  called  in  German  raw  work 
(Roharbeit),  because  the  ores  are  subjected  to  this 
process  raw,  without  preparation.  The  object  is,  as 
before  mentioned,  to  concentrate  the  silver  in  a  small 
quantity  of  matt  or  sulphides  (Germ.  Rohstein),  by 
means  of  iron  pyrites  or  heavy  spar  (if  the  ore  does  not 
contain  already  a  sufficient  quantity  of  sulphur),  while 
the  earthy  substances  and  foreign  oxyds  of  metals  are 
15 


226  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

scorified.    In  melting  for  matt  the  following  rules  must 

be  observed  : 

1.  The  mixture  of  ore  and  fluxes  must  be  prepared 
so  that: 

a.  A  certain  quantity  of  matt  is  obtained  in  propor- 
tion to  the  amount  of  silver  in  it. 

b.  A  proper  fluid  slag  is  formed. 

In  regard  to  the  proportion  of  matt  to  the  amount  of 
silver,  the  concentration  must  be  limited  from  forty  to 
sixty  ounces  per  ton,  according  to  experience,  other- 
wise a  considerable  loss  of  silver  might  occur.  The  loss 
is  a  mechanical  one  which  cannot  be  avoided,  caused  by 
small  particles  of  matt  becoming  involved  in  the  slag. 
To  produce  a  rich  matt,  it  requires  a  smaller  quantity  of 
iron  pyrites  in  consequence  of  which  the  silver  cannot 
be  collected  perfectly  remaining  exposed  to  scorification. 

The  most  suitable  amount  of  matt  in  the  ore  is 
between  thirty  and  fifty  per  cent,  of  the.  prepared  ore. 
This  amount  must  be  obtained  by  a  proper  proportion 
of  pyritous  ore  or  by  addition  of  iron  pyrites.  If  the 
ore  is  found  to  be  too  rich  in  pyrites,  some  sulphur 
must  be  driven  out  by  roasting.  Some  copper  pyrites 
is  advantageous,  it  imparts  to  the  iron  pyrites  a  greater 
collective  ability  and  separates  better  from  the  slag; 
but  a  copperous  matt  is  more  difficult  to  treat  with  lead 
for  the  purpose  of  silver  extraction.  Arsenical  pyrites 
and  zinc  blend,  if  in  considerable  quantity,  are  injurious, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  227 

weakening  the  collective  power  of  the  matt.  The  first 
causes  a  loss  of  silver  by  its  volatility,  the  second  pro- 
duces a  tough  melting. 

The  quantity  of  matt  in  the  prepared  ore  is  ascer- 
tained by  the  assay  for  matt.  For  this  purpose,  one-half 
ounce  of  borax  glass,  one-half  ounce  powdered  glass, 
twenty-four  grains  of  resin,  well  mixed  with  one-half 
ounce  of  ore  are  introduced  into  a  crucible  and  covered 
with  one  and  one-half  ounces  of  common  salt.  This  mix- 
ture is  melted  for  about  half  an  hour,  applying  a  strong 
heat.  The  matt  button  obtained  must  be  weighed 
directly,  as  it  falls  to  powder  after  some  time. 

If  substances  with  a  small  amount  of  sulphur  are 
assayed  for  matt,  some  metallic  copper  must  be  added 
to  the  above  mixture.  The  regulus  separates  easily  from 
the  slag.  The  added  copper  must  be  subtracted  from 
the  weight  of  the  regulus. 

As  mentioned  under  b,  care  must  be  taken  to  obtain 
a  fluid  slag  in  melting  the  ore,  in  order  to  facilitate  the 
separation  of  matt.  This  depends  on  the  right  propor- 
tion" of  the  substances  producing  the  slag.  Ores  abound- 
ing in  earthy  substances,  are  prepared  with  ferriferous 
ores  or  roasted  iron  pyrites ;  some  lime  is  also  added, 
especially  if  a  great  deal  of  quartz  is  present.  Iron  slag 
gives  also  a  good  flux.  A  favorable  scorifying  substance 
is  found  in  the  single  silicate  slag,  resulting  from  melting 
lead  ores.  The  melting  for  matt  is  in  the  best  condition, 
if  a  slag  is  obtained  between  bi-  and  singulo  silicate, 
which  permits  an  easy  separation  of  the  matt,  without 


228  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

stiffening  too  quick.  This  mode  of  melting  is  more  dif- 
ficult if,  in  absence  of  iron  pyrites,  ponderous  spar  is 
used. 

The  melting  is  performed  with  charcoal  or  coke,  in 
either  blast  or  reverberating  furnaces.  The  blast  fur- 
naces are  provided  with  one,  two,  or  more  tuyeres,  and 
with  dust  chambers.  A  furnace  with  two  tuyeres  melts 
more  ore  than  with  one,  and  consumes  also  less  fuel. 
Reverberating  furnaces  have  several  advantages  over 
the  blast  furnaces,  but  yield  a  richer  matt  in  zinc,  when 
blend  containing  ore  is  worked.  This,  however,  can  be 
remedied  with  an  addition  of  charcoal  and  roasted  ore 
containing  oxyd  of  iron.  Heated  compressed  air  favors 
the  melting  and  effects  saving  of  fuel. 

II.    EXTRACTION  OF  SILVER  FROM  IRON,  COPPER,  AND  LEAD 
MATTS  BY  MEANS  OF  LEAD. 

The  desilverization  of  the  matts  can  be  performed : 

1.  Treating  the  matt  in  unroasted  condition  with 
metallic  lead,  or  substances  containing  oxyd  of  lead,  or 
with  galena  and  metallic  iron. 

2.  By  melting  the  roasted  matt  with  roasted  or 
unroasted  lead  ores,  litharge,  and  hearth. 

3.  By  melting  of  roasted  lead  matt  either  by  itself  or 
with  metallic  iron. 

Treatment  of  unroasted  matt  with  metallic  lead,  is 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  229 

based  on  the  nature  of  metallic  lead  to  decompose  the 
sulphides  of  silver,  forming  sulphide  of  lead.  The  sep- 
arated silver  is  taken  up  by  the  surplus  lead.  The  desil- 
verization  is  obtained  more  perfectly  if  a  better  contact 
between  lead  and  matt  is  effected,  but  a  perfect  extrac- 
tion cannot  be  accomplished,  unless  by  repeated  melting 
with  fresh  lead.  In  this  case,  the  black  copper,  obtained 
from  the  matt  is  not  subjected  to  the  liquation.  This 
procedure  is  generally  adopted  where  no  lead  ore  can 
be  got.  In  melting  the  matt  with  lead  ores  in  blast  fur- 
naces, the  desilverization  of  the  matt  is  more  perfect,  but 
a  greater  loss  in  lead  and  copper  will  result,  than  by 
treating  the  matt  with  metallic  lead  at  a  lower  temper- 
ature. 

There  are  only  two  ways  for  the  treatment  of  matt 
with  lead — The  hydrostatic  melting,  and  melting  of  lead 
with  matt: 

A.  The  Hydrostatic  Melting — or  melting  through  a 
column  of  lead.  The  operation  will  succed,  if  the  matt 
is  conducted  through  the  lead  by  drops.  The  matt  must 
press  on  the  lead  with  greater  weight  than  the  weight 
of  the  lead  itself.  It  is  therefore  necessary  to  have  the 
tuyere  at  the  proper  height  above  the  front  hearth.  To 
find  the  pressing  height  of  the  melted  masses  (matt  and 
lead)  we  must  observe,  for  example,  the  melted  matt  in 
the  furnace  =  a,  the  specific  gravity  of  the  matt  =  5, 
and  the  gravity  of  the  lead  ==  c.  If,  for  instance,  the 
height  of  the  copper  matt  column  a  =  30  inches,  b  =  5*0, 


230 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


and  c  =  11*33,  and  %,  the  desired  height  of  the  front 
hearth,  which  is  to  be  filled  with  lead,  the  answer  would 
be: 

x  :  a  =  b  :  c,  or, 
x=aXb  30X5-0 

-^=TT33-=13'2  mches' 

Plumbiferous  matt  is  less  suitable  for  this  operation 
than  matt  containing  arsenic  and  antimony.  Generally, 
this  hydrostatic  melting  with  suitable  copper  matt,  com- 
pared with  the  liquation,  suffers  a  smaller  loss  in  copper 
and  lead,  but  the  desilverization  is  not  so  perfect.  In 
deciding  for  the  preference  of  these  two  modes,  the  ques- 
tion must  be  considered  whether  the  value  of  the  greater 
quantity  of  obtained  lead  and  copper  covers  the  value  of 
the  less  quantity  of  extracted  silver. 

B.  The  Fusion  of  Lead  and  Matt. — The  fused  matt  is 
stirred  and  mixed  with  the  melted  lead  in  a  hearth  pre- 
pared for  tapping.  The  hearths  are  of  different  sizes, 
about  four  and  one-half  feet  in  diameter,  and  three  feet 
deep.  The  hearth  is  provided  with  a  pair  of  bellows. 
The  matt  is  first  melted  down  on  charcoal,  then  the  lead, 
which  sinks  through  the  matt  to  the  bottom,  taking  up 
silver  from  the  matt.  Four  hundred  pounds  of  matt  are 
treated  with  about  seventy-five  pounds  of  lead.  When 
all  the  lead  is  melted,  it  must  be  mixed  for  a  while  with 
the  matt  by  means  of  an  unseasoned  wooden  rod,  and 
the  lead  tapped.  The  matt  must  be  treated  with  lead 
repeatedly,  three  or  four  times  over.  The  lead  of  the 
first  tapping  is  ready  for  cupellation,  but  that  from  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  231 

following  is  used  over  again  for  the  extraction,  till  the 
silver  concentrates  to  about  three  hundred  ounces  per 
ton,  when  it  is  considered  rich  enough  to  be  cupelled. 

LEAD  MANIPULATION  WITH  ARGENTIFEROUS  BLACK 
COPPER  (LIQUATION). 

Sec.  70.  Argentiferous  Black  Copper — Is  produced,  if 
the  copper  ores,  or  the  matts  are  so  poor  in  silver  that 
the  treatment  with  lead  is  not  advantageous.  In  this  case 
the  silver  is  purposely  concentrated  in  black  copper. 
Argentiferous  black  copper  is  also  obtained  from  melt- 
ing of  argentiferous  galena  containing  some  copper  ore, 
or  from  working  argentiferous  copper  ores,  or  matts  with 
lead.  Although  the  greatest  part  of  the  silver  is 
extracted  from  these  substances  by  the  lead,  the  copper 
always  retains  some  silver  as  long  as  sulphur  is  present. 

The  separation  of  silver  from  copper  can  be  executed 
in  different  ways.  One  of  the  oldest  methods  is  the 
liquation.  Argentiferous  copper  is  melted  with  a  certain 
proportion  of  lead.  In  cooling,  a  great  part  of  the 
silver  containing  lead  separates,  forming  then  a  mixture 
of  argentiferous  lead  and  an  alloy  of  about  one  part 
lead  with  three  parts  copper,  and  considerably  less  sil- 
ver. Heated  to  the  melting  point  of  lead,  the  latter, 
with  the  silver,  flow  out,  leaving  the  alloy  of  copper  and 
one  part  of  lead  in  unmelted  spongy  condition,  retain- 
ing its  original  shape. 

This  method  is  defective,  not  permitting  a  perfect  sep- 


232  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

aration  of  silver3  and  suffers  a  great  loss  in  silver,  cop- 
per, and  lead.  A  great  many  products  result  from  this 
operation,  so  that  the  liquation  process  appears  endless. 
For  this  reason,  in  most  places,  other  processes  are  now 
adopted,  by  which  the  silver  from  the  matts  is  extracted 
in  a  more  perfect  way.  In  Freiberg  (Saxony)  Augus- 
tin's  method  is  adopted.  In  Mansfeld,  the  liquation  was 
replaced,  first,  by  amalgamation  of  the  copper  matt,  then 
by  Augustin's,  and  finally  by  Ziervogel's  extraction. 
According  to  Karsten,  the  cost  for  liquation  of  one  hun- 
dred pounds  of  black  copper,  is  equal  to  the  value  of 
four  or  four  and  a  half  ounces  of  silver,  so  that  black 
copper  with  eighty  or  ninety  ounces  per  ton,  would  not 
pay  the  liquation.  This  is  the  reason  that  some  copper 
of  commerce  contains  a  great  deal  of  silver.  In  some 
places,  however,  copper  with  forty-five  to  fifty  ounces  o 
silver  per  ton,  was  subjected  to  liquation  with  profit. 

But  the  expense  of  liquation  increases,  not  only  at  a 
very  low  amount  of  silver,  but  also  when  the  copper  is 
rich.  The  reason  is  that  in  this  case,  if  the  copper  con- 
tains, for  instance,  twenty  per  cent,  of  silver,  the  liqua- 
tion must  be  often  repeated,  in  order  to  extract  as  much 
silver  as  possible.  The  operation  becomes  extended,  so 
that  the  loss  of  silver  must  increase.  The  cost  of  liqua- 
tion of  one  hundred  pounds  of  copper  will  be  more  than 
the  value  of  the  four  and  a  half  ounces  of  silver. 

The  black  copper  is  first  broken  in  small  pieces  cold, 
or  it  is  made  red-hot,  which  facilitates  the  breaking,  or 
it  is  melted  and  poured  into  cold  water  (granulated), 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  233 

and  then  melted  with  lead.  Each  ounce  of  silver  requires 
thirty  to  thirty-two  pounds  of  lead,  but  the  proportion 
of  lead  to  copper  should  not  be  over  11 :  3.  Lead  and 
copper  in  the  proportion  of  eleven  to  three,  in  regard  to 
the  above  mentioned  proportion  of  lead  and  silver,  are 
melted  in  a  cupola  furnace  with  aid  of  the  bellows.  The 
alloy  is  poured  into  moulds,  assuming  the  shape  of  a 
disk  eighteen  inches  in  diameter,  and  from  three  to  three 
and  a  half  inches  thick. 

These  copper  disks  are  laid  on  two  inclined  iron  plates 
in  an  oven,  in  such  a  way  that  a  space  of  one  or  two 
inches  is  left  between  each  disk.  They  are  covered  with 
charcoal,  and  it  ignited.  The  lead  soon  commences  to 
trickle  from  the  disks,  and  runs  on  the  inclined  iron 
plates,  through  the  split  which  is  left  between  them  into 
a  basin  underneath.  When  the  lead  ceases  to  flow,  the 
operation  is  finished.  The  lead  is  given  over  to  the 
cupellation.  The  spongy  copper  contains  from  ten  to 
twenty  per  cent,  of  lead.  If  this  copper  is  found  to  be 
rich  in  silver,  it  is  fused  again  with  lead  and  treated  as 
before.  If  otherwise,  it  is  subjected  to  the  sweating 
process. 

The  sweating  is  performed  in  another  furnace  at  a 
stronger  heat,  to  get  rid  of  another  portion  of  lead, 
which  however  is  obtained  in  an  oxydized  condition. 
The  unfused  copper  is  purified  on  a  refining  hearth. 

Extraction  of  Silver  by  Copper  and  Lead. 
The  object  of  this  process  is  the  decomposition  of  the 


234  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

sulphides  of  silver  in  the  ores  and  matts,  combined 
with  an  extraction  of  silver  by  lead.  The  decomposition 
of  silver  sulphurets  by  copper  is  not  perfect  for  the 
reason  that  when  copper  prevails,  an  alloy  of  silver, 
copper,  and  matt  is  formed  which  retains  a  great  deal  of 
sulphide  of  silver.  If  there  is  also  lead  in  the  ore  or  in 
the  melting  product,  this  will  be  eliminated  with  the 
silver  while  an  equivalent  quantity  of  copper  enters 
the  matt. 

Copper-Dissolving  Process. 

The  principle  of  this  process  is  as  follows:  If  ar- 
gentiferous matt  is  melted  together  with  copper  and 
plumbiferous  products,  the  copper  enters  the  mat 
while  the  eliminated  silver  is  taken  up  by  the  lead. 
At  the  same  time  the  lead  acts,  desilvering  the  matt. 
If  too  much  copper  is  added  it  does  not  remain  dissolved 
in  the  matt,  but  separates  partly  again,  and  enters  the 
lead.  If  the  copper  contains  silver,  this  will  be  also 
extracted,  so  that  the  copper  need  not  be  subjected  to 
another  extraction,  for  instance,  by  liquation  or  amal- 
gamation. The  usefulness  of  this  process  depends  gen- 
erally on  local  circumstances,  especially  on  the  propor- 
tion of  matt  and  black  copper,  which  is  obtained  in 
melting.  If  too  much  matt,  then  the  extraction  o 
silver  is  imperfect ;  on  the  contrary,  if  too  little,  the 
black  copper  cannot  all  be  dissolved  by  the  matt,  but 
alloys  with  the  lead. 

Under  suitable  circumstances,  this  process  is  advan- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  235 

tageous.  It  is  preferable  to  the  liquation  process, 
because  it  allows  a  more  perfect  desilverization  of  the 
matts. 

SEPARATION  OF  SILVER  FROM  ARGENTIFEROUS 

LEAD. 

CUPELLATION  OF  PlG  LEAD. 

Sec.  71.  Cupellation,  the  object  of  separating  silver 
from  argentiferous  lead,  is  executed  in  such  a  way  that 
the  lead  on  the  hearth  of  an  oven,  under  influence  of 
heat  and  compressed  air,  is  converted  by  degrees  into 
an  oxyd  of  lead  (litharge)  which  draws  to  the  periphery 
from  the  convex  surface  of  the  fused  lead,  exposing 
thus  the  metal  constantly  to  the  oxygen  of  the  air. 
Drawing  off  this  litharge  as  it  is  formed,  the  silver 
finally  remains  in  the  hearth. 

The  old  cupelling  furnace  has  no  separate  fire-place, 
but  the  lead  was  melted  in  the  hearth  between  fire- 
wood ;  the  blast  was  directed  on  the  lead,  over  which 
burning  wood  was  maintained  till  the  process  was 
finished.  This  mode  requires  much  more  fuel  and  the 
oxydation  of  lead  is  imperfect. 

There  are  two  modes  of  cupelling  in  use :  The  Ger- 
man on  fixed  hearths,  and  the  English  on  movable 
tests. 

Cupellaiion  in  immovable  Hearths. — The  German  cupel- 
ling-furnaces  are  constructed  of  two  principal  parts ;  of 


236  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  fire-room  and  of  the  cupelling-room,  connected  by  a 
fire-bridge.  The  cupelling  room  is  formed  by  a  circular 
block  of  mason-work  about  fifteen  inches  above  the 
ground,  provided  with  ■  channels  for  the  escape  of  mois- 
ture. On  the  periphery  of  the  block,  the  wall  from 
twelve  to  fifteen  inches  thick  is  carried  up  twenty 
inches,  forming  a  wall-ring,  of  which  the  inner  space 
receives  the  material  for  the  hearth.  The  coppel  or 
hood  is  formed  of  many  iron  bars  well  riveted,  and  with 
many  little  hooks  for  the  purpose  of  holding  the  clay 
lining.  There  have  been  also  clay  coppels  in  use, 
weighing  over  a  ton  ;  the  iron  ones,  from  1,100  to  1,300 
pounds,  are  generally  preferable  for  many  reasons.  By 
means  of  a  crane,  three  coppels  can  be  lifted  and  turned 
aside.  Arches  of  brick,  used  in  some  places,  are  less 
convenient.  They  must  form  high  coppels  (five  and  a 
half  feet)  to  resist  the  effect  of  heat  and  lead  fumes 
longer ;  they  are  a  great  deal  cheaper,  but  the  iron 
ones  stand  ten  times  as  long.  The  iron  skeleton  of  the 
coppel  is  lined  first  with  loam,  then  with  a  mixture  two 
inches  thick  of  three  parts  of  clay  and  one  part  of 
quartz. 

In  the  wall-ring,  coarse  slag  is  introduced  or  rock  of 
the  size  of  one's  fist,  about  twelve  inches  deep  in  the 
centre,  and  sixteen  to  eighteen  inches  deep  on  the  sides, 
forming  a  concave  surface.  Over  the  slag  comes  a  row 
of  brick  and  then  the  hearth-mass.  Lixiviated  wood- 
ashes  are  not  much  in  use,  but  replaced  by  the  marl 
which  is  a  much  better  hearth  material.    The  marl  is 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  237 

cheaper,  it  does  not  absorb  so  much  litharge,  and  the 
result  in  regard  to  the  quantity  of  silver  is  always 
better  than  on  a  test  of  ashes.  It  is  pulverized  and 
sifted  through  a  sieve  of  about  sixty-four  holes  to  the 
square  inch,  then  very  evenly  moistened,  introduced  in 
the  hearth  and  stamped  hard  from  four  to  six  inches 
thick.  The  whole  mass  may  be  introduced  at  once,  or 
in  portions.  The  hearth  must  be  hard  enough  so  that 
no  impression  can  be  made  with  the  finger.  The  con- 
cave hearth  in  the  centre  is  six  to  eight  inches  deep 
and  from  six  to  ten  feet  in  diameter. 

The  wall-ring  is  continued  about  two  feet  and  a  half 
above  the  hearth,  and  contracted  for  several  inches  on 
the  top,  on  which  the  coppel  rests.  This  ring  has  several 
apertures :  one  litharge  hole,  another  hole  opposite  the 
fire-bridge  through  which  the  lead  is  introduced,  and 
two  holes  for  the  tuyeres. 

The  hearth  is  charged  either  at  once  with  so  much 
lead  as  is  intended  for  one  trip,  from  five  to  twelve 
tons,  or  is  filled  with  lead,  and  more  added  during  the 
operation,  in  the  same  proportion,  as  litharge  is  drawn 
off.  The  latter  way  is  preferable  for  this  reason,  that  a 
smaller  hearth  can  be  used  and  less  wood  consumed  on 
the  same  quantity  of  lead.  A  large  hearth  must  be 
kept  at  a  higher  heat.  This  makes  the  hearth  softer, 
and  the  mass  absorbs  more  litharge.  But  the  addition 
of  lead,  during  cupellation,  yields  an  impure  litharge 
which,  when  reduced,  renders  a  low  quality  of  lead. 

When  the  lead  is  charged,  the  coppel  is  placed  on 


238  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  wall-ring,  all  clefts  and  little  cracks  are  covered 
with  loam  and  a  slow  fire  started.  By  increased  heat, 
the  lead  melts  down,  leaving  all  impurities  on  the 
surface.  These  impurities  or  dry  scrapings  (German, 
Abzug)  are  skimmed  off.  They  contain  a  great  deal  of 
lead,  copper,  antimony,  arsenic,  also  silver  in  oxydized 
and  sulphuretted  condition.  If  the  pig  lead  is  of  pure 
quality,  the  scrapings  are  not  regarded.  The  surface  of 
the  lead  after  the  removal  of  the  dry  scrapings  does  not 
remain  clear  for  a  long  time,  but  becomes  again  coated 
by  a  crust. 

This  crust,  after  the  drawing  of  dry  scrapings  or  after 
the  melting  of  pure  pig  lead,  must  be  scorified  by  in- 
creased heat  and  brought  into  fusion,  admitting  at  the 
same  time  the  blast.  The  fused  crust  or  black-litharge 
scrapings,  or  froth  (German,  Abstrich),  must  be  drawn 
off  likewise.  In  the  commencement  it  is  spongy,  black, 
has  an  imperfect  metallic  lustre,  but  assumes  a  gray 
greenish-yellow  color  at  the  end  of  the  period.  It  con- 
tains metallic  and  oxydized  lead,  besides  oxyds  of  zinc, 
iron,  bismuth,  antimony,  arsenic,  etc. ;  the  antimony 
especially  concentrates  in  it  to  a  considerable  amount. 

Dry  scrapings  and  the  black  litharge  contain  more 
silver  than  the  litharge.  The  main  part  of  the  com- 
pound is  oxyd  of  lead  which  has  the  property  of  taking 
up  the  sulphides  of  antimony  and  arsenic,  by  which 
again  the  sulphides  of  copper  and  silver  are  brought 
into  the  combination. 

While  the  black  litharge  is  drawn,  heat  and  blast 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  239 

must  be  increased,  in  order  to  hasten  the  scorification. 
To  facilitate  the  drawing,  some  moistened  coarse  char- 
coal is  thrown  on  the  surface  by  which  the  froth  assumes 
a  spongy  condition,  when  it  is  easily  removed.  The 
quantity  of  this  froth  depends  on  the  quality  of  the 
lead. 

When  the  black  color  of  the  froth  changes  into 
greenish-brown,  assuming  a  more  tough  consistency, 
the  oxyds  of  zinc,  iron,  and  copper  are  mostly  removed, 
and  the  black  litharge  consists  in  the  greatest  part  only 
of  the  oxyds  of  lead  and  antimony.  The  more  the  latter 
is  eliminated  the  more  the  yellow  color  of  the  oxyd  of 
lead  appears.  The  tough,  scori-like  condition  disappears, 
and  a  short,  scaly  state  appears.  The  mass  flows  no 
more  down  the  floor,  but  hardens  in  front  of  the  furnace. 
As  soon  as  this  change  appears  the  drawing  of  froth  is 
finished,  and  the  temperature  must  be  lowered. 

The  breast  of  the  furnace  or  the  litharge-bridge  is 
cleaned,  then  a  channel  cut  or  scratched  by  an  iron 
hook  or  saw-like  instrument.  Through  this  channel  the 
litharge  runs,  wherein  it  is  driven  by  the  blast.  The 
litharge  channel,  at  a  proper  cupellation  should  be  cut 
so  deep  only  that  the  litharge  ceases  to  flow,  when  the 
wind  is  stopped.  The  formation  of  litharge  is  difficult, 
if  the  antimony  does  not  depart  with  the  black  litharge, 
because  the  lead  has  little  inclination  to  oxydize  before 
the  antimony.  This  explains  the  long  duration  of  some 
cupellations. 

Generally  the  temperature  must  be  kept  as  moderate 


240  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

as  possible,  otherwise  more  lead  and  silver  will  volatilize. 
A  hot  litharge  also  eats  the  channel  too  much,  and  causes 
the  escape  of  some  lead.  If  the  cupellation  is  kept  too 
cold,  the  silver,  which  is  in  the  unsufficiently  liquid 
litharge,  cannot  come  in  contact  well  enough  with  the 
lead  to  be  reduced  again,  consequently  the  litharge 
from  too  cold  cupellation  becomes  richer  in  silver.  At 
a  too  high  temperature,  more  litharge  is  absorbed  by 
the  hearth,  which  is  injurious,  but  this  cannot  be  avoided 
entirely  even  by  the  best  conducted  heat. 

On  the  edge  of  the  bath,  by  escaping  moisture  and 
carbonic  acid  of  the  hearth  a  throwing  up  of  bubbles  is 
created,  which  follow  the  edge  of  the  bath  when  the 
periphery  of  the  lead  decreases.  The  bubbles  cease 
shortly  before  the  brightening  or  concentration  in  the 
centre.  It  indicates  too  much  heat  if  this  boiling  is 
violent,  but  it  should  not  be  too  weak. 

Care  must  be  taken  to  keep  always  a  sufficient 
quantity  of  litharge  on  the  periphery  of  the  lead-bath. 
The  blast  can  be  regulated  in  any  required  direc- 
tion. In  the  first  part  of  cupellation  the  blasts  (of  two 
tuyeres)  have  a  divergent  direction.  According  to  the 
different  position  of  the  litharge  the  direction  can  be 
modified.  At  the  end  of  the  operation  the  blasts  may 
cross  each  other.    Hot  air  did  not  answer  in  all  places. 

The  addition  of  lead  commences  as  soon  as  a  good 
run  of  litharge  is  observed.  It  is  introduced  by  the 
feed-hole  and  placed  on  the  brim  of  the  hearth.  Time 
and  quantity  of  feeding  depend  on  the  progress  of 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  241 

cupellation,  and  are  indicated  by  the  litharge  and  lith- 
arge-channel. At  the  end  of  the  operation  when  less 
litharge  is  formed,  the  bath  assumes  a  bright  color. 
This  is  an  indication  that  the  period  of  brightening  is 
approaching.  The  bath  becomes  covered  with  a  net-like 
coat,  movable  on  the  convex  surface,  consisting  of  lith- 
arge-spots, between  which  the  silver  glances  through. 
These  spots  grow  larger,  till  at  last  the  net  breaks  and 
the  litharge  slides  to  the  sides,  producing  a  peculiar 
shine  which  is  called  the  brightening,  distinguished  by  a 
play  of  colors.  The  colors  are  produced  by  the  separa- 
tion of  the  last  of  the  oxyd  of  lead  in  very  thin  layers, 
through  which  the  light  passes,  being  reflected  by  the 
silver  under  a  certain  color.  The  kind  of  color  depends 
on  the  thickness  of  the  coating,  which  grows  gradually 
towards  the  silver  of  the  convex  surface,  producing  the 
variety  of  colors,  in  a  certain  system.  This  is  going  on 
as  long  as  oxyd  of  lead  is  emitted,  and  ceases  when  the 
silver  becomes  fine.  The  purification  can  continue 
under  a  strong  heat,  till  to  the  required  fineness,  which 
in  large  furnaces  however  is  not  done  on  account  of  the 
consume  of  fuel  by  which  the  extensive  space  must  be 
kept  at  a  high  temperature.  The  silver  is  generally 
taken  out  after  the  brightening,  and  the  five  or  ten  per 
cent,  of  foreign  substances  which  are  left  in  it,  separated 
by  refining. 

After  the  brightening  the  wind  is  stopped,  the  silver 
cooled  first  with  warm  then  with  cold  water  and  finally 
broken  out  by  means  of  a  long  chisel. 
16 


242  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

The  products  of  cupelling  are  the  following : 

a.  The  black  litharge,  or  froth,  is  a  very  impure,  ferrif- 
erous and  copperous  litharge,  obtained  in  the  first  part 
of  the  operation.  This  litharge  is  not  suitable  for  the 
market,  neither  for  the  reduction  process.  Generally  it 
is  melted  with  the  ores.  The  bla'ck  litharge  contains 
sometimes  as  much  lead  as  the  yellow.  The  first  lith- 
arge shows  generally  a  brown  or  greenish  color,  caused 
by  iron  and  copper.  The  affinity  of  copper  and  lead  to 
the  oxygen  seems  to  be  equal,  as  there  is  always  some 
copper  in  the  litharge  from  the  beginning  to  the  end  of 
the  process. 

b.  The  poor  litharge  is  the  second  litharge.  It  first 
looks  yellow,  but  on  getting  cold,  cracks  in  all  direc- 
tions. In  the  clefts  arises  a  red,  scaly,  easily  pulverizing 
product  (the  red  litharge)  while  the  rapidly-cooled  crust 
retains  its  color  and  cohesion  (the  yellow  litharge).  The 
red  litharge  is  the  same  chemical  combination  as  the 
yellow,  in  an  isomeric  modification,  differing  only  by 
structure  and  color.  The  production  of  the  red  litharge 
can  be  promoted  by  drawing  the  litharge  from  the 
cupelling  furnace  into  hollow  cylinders  of  sheet-iron,  in 
which  it  cools,  assuming  a  red  color  and  the  fine  condi- 
tion. This  is  the  best  article  for  the  market.  The 
yellow  litharge  is  quite  suitable  for  reduction. 

c.  The  Rich  Litharge. — This  product  is  obtained  in  the 
last  hours  of  cupellation.  Being  richer  in  silver  this 
litharge  is  never  sold  but  melted  with  the  ore. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  243 

d.  The  Silver. — The  fineness  of  the  cupelled  silver 
depends  entirely  on  the  time  consumed  after  bright- 
ening. 

e.  The  Hearth. — The  hearth  always  retains  more  silver 
than  the  litharge,  the  silver  of  which  is  taken  up  by 
the  lead  during  the  longer  contact.  This  is  not  the 
case  with  that  litharge  which  draws  into  the  hearth- 
mass.  When  the  cupellation  is  finished  and  the  furnace 
cooled  down,  the  hearth  is  broken  out  and  the  heavy 
part,  saturated  with  oxyd  of  lead,  given  over  to  the 
melting  manipulation. 

Cupellation  in  Movable  Hearths. — This  mode  is  prac- 
ticed chiefly  in  England.  These  cupelling-furnaces 
differ  from  the  German  in  two  points :  firstly,  they 
have  a  fixed  flat  arch ;  secondly,  the  hearth-mass  is 
generally  bone-ash.  The  tests  are  prepared  outside  of 
the  furnace  in  oval  iron  test-rings,  four  feet  in  the 
larger  and  two  and  a  half  feet  in  the  smaller  diameter. 
These  tests  are  placed  into  the  furnace  from  beneath, 
leveled,  and  the  room  between  the  test-ring  and  furnace- 
wall  filled  with  fire-proof  material.  Generally,  the  Eng- 
lish pig  lead  is  so  poor  in  silver  that  it  must  be  concen- 
trated by  Pattinson's  crystallization  process. 

Fine,  pulverized  bone-ashes  are  moistened  with  water 
containing  some  potash,  then  introduced  into  the  test- 
ring  and  beaten  in.  The  test  is  so  cut  out  that  the 
brim  above  is  two  inches,  and  at  the  bottom  three  inches 
thick,  and  the  bottom  itself  one  inch.    On  the  front 


244  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

side  the  test  brim  is  five  inches  wide,  containing  an 
opening  for  the  litharge. 

The  test  is  brought  into  the  furnace,  dried,  and  then 
heated  to  red  heat.  The  lead  is  introduced  in  fused 
condition,  and  the  temperature  raised  till  the  crust 
melts,  when  the  blast  is  thrown  in,  by  which  the  lith- 
arge is  driven  to  the  front.  By  the  addition  of  fused 
lead,  the  surface  is  always  kept  at  the  same  level,  till 
about  five  tons  of  lead  are  cupelled.  The  cupelling  is 
then  so  far  continued  that  the  alloy  may  contain  two 
or  three  hundred  times  as  much  lead  as  silver,  where- 
upon the  alloy  is  tapped,  the  tap-hole  shut  and  the  con- 
centration continued  in  the  same  way.  When  so  much 
rich  lead  is  obtained  that  a  silver-cake  of  from  3,000  to 
5,000  ounces  can  be  expected,  the  cupellation  on  it  is 
executed  in  the  described  way. 

Heated  steam  in  place  of  wind  yields  a  finer  litharge. 

CONCENTRATION  OF  SILVER  IN  POOR  PIG  LEAD, 
By  Pattinson's  Crystallization  Process. 

Sec.  72.  Most  of  the  English  pig  lead  is  poor,  being 
produced  from  galena,  generally  under  twenty  ounces 
per  ton.  The  silver  of  such  poor  lead  could  not  be 
extracted  advantageously  prior  to  the  year  1833,  when 
Lee  Pattinson  patented  a  new  mode  of  concentrating 
the  silver  in  argentiferous  lead.  This  procedure  permits 
the  extraction  if  the  ore  contains  only  three  ounces  of 
silver  per  ton. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  245 

This  method  is  founded  on  the  fact  that  if  an  alloy  of 
lead  and  silver  is  melted  in  an  iron  kettle  and  cooled, 
while  often  stirred,  lead  crystals  will  form  at  a  certain 
temperature  which  are  poorer  in  silver  than  the  remain- 
ing liquid.  The  crystals  are  removed  by  means  of  per- 
forated ladles,  and  several  repetitions  of  the  same  pro- 
cess on  the  crystals  and  the  enriched  lead  will  yield  a 
very  poor  lead  of  commerce  and  a  rich  part  for  the 
cupellation. 

Besides  the  advantage  of  being  enabled  to  extract 
small  quantities  of  silver,  this  process  yields  also  a  purer 
and  more  valuable  lead  than  that  of  reduced  litharge. 
Although  the  cupellation  of  the  enriched  lead  sustains 
a  loss  of  at  least  five  per  cent,  of  lead,  the  average  is 
nevertheless  below  two  per  cent.,  while  the  cupellation 
of  the  whole  mass  would  suffer  from  seven  to  eight  per 
cent,  loss  of  lead.  Yery  little  or  nothing  is  saved,  com- 
paratively, in  fuel  and  labor.  This  process  requires 
strong  rather  than  skillful  hands. 

Lead,  containing  about  five  ounces  per  ton,  offers,  the 
best  advantage.  At  a  higher  amount  of  silver  the 
expenses  for  labor  and  fuel  increase,  and  the  process  is 
considerably  delayed,  still  in  many  places  lead  with 
from  forty  to  fifty  ounces  is  concentrated  with  pecu- 
niary advantage.  Impure  lead,  containing  antimony, 
arsenic,  zinc,  or  copper,  is  not  suitable  for  concentra- 
tion, the  separation  of  silver  being  imperfect.  Such 
lead  is  first  purified  by  continued  heating  in  a  reverber- 


246  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

atory  furnace  or  by  stirring  in  a  kettle  with  an  unsea- 
soned rod,  and  skimming  off  the  impurities. 

The  good  result  of  this  process  depends  also  on  the 
right  conduction  of  the  temperature.  If  this  be  too  low, 
the  separation  of  crystals  cannot  take  place,  because  the 
whole  mass  stiffens  too  soon.  On  the  contrary,  if  too 
hot,  no  crystals  can  arise.  Only  a  large  quantity  of 
lead  will  give  a  good  result,  because  the  transition  of 
the  liquid  into  the  stiff  state  is  only  slow  enough  in  a 
large  quantity  to  give  sufficient  time  for  the  removing 
of  the  crystallized  lead.  Many  experiments  have  failed 
because  operated  with  too  small  quantities. 

Generally,  in  England,  such  lead  is  concentrated  as 
contains  from  five  to  ten  ounces  of  silver  per  ton,  in 
lots  of  from  2*5  to  five  tons  in  four  or  nine  cast-iron 
kettles,  taking  about  fifty  tons  for  one  trip  in  succession. 
It  requires  several  days  to  work  up  this  quantity  with 
two  or  four  men. 

At  a  battery  of  nine  kettles,  for  instance,  the  lead  with 
about  ten  ounces  silver  per  ton  is  introduced  in  one  of 
the  middle  kettles,  and  cooled  down  after  it  has  been 
melted.  The  crust  from  the  sides  of  the  kettle  is  thrust 
into  the  liquid  lead  by  means  of  an  iron  paddle,  stirring 
at  the  same  time  the  mass.  With  an  iron  perforated 
ladle  (of  which  the  handle  is  nine  feet  long,  the  ladle 
from  twelve  to  fifteen  inches  diameter,  six  inches  deep, 
with  three-quarter  inch  holes  in  the  bottom),  the  crystal- 
lized lead  is  dipped  from  the  bottom  of  the  kettle,  and 
after  the  liquid  lead  drops  off  by  shaking  the  ladle,  it  is 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  247 


laded  into  the  next  kettle  on  the  left.  This  is  done  till 
about  of  the  original  quantity,  with  an  average 
amount  of  five  ounces  silver  is  transferred.  The  next 
1°L5  with,  about  ten  ounces  silver,  is  laded  temporarily 
into  a  flat  kettle.  The  last  with  twenty  ounces  of 
silver  is  transferred  to  the  first  kettle  on  the  right.  The 
lead  from  the  flat  kettle  with  ten  ounces  of  silver,  is 
introduced  again  into  the  first,  with  another  portion  of 
the  original  lead,  and  proceeded  with  in  the  same  way 
as  long  as  there  is  lead  of  ten  ounces  of  silver  at  hand. 

As  soon  as  the  kettle  with  the  crystals  on  the  left  with 
five,  and  the  kettle  on  the  right  side  with  the  enriched 
lead  containing  twenty  ounces  of  silver  per  ton,  are  filled, 
the  separation  is  executed  in  both,  and  afterwards  in  all 
the  following  kettles,  in  the  same  manner  as  it  was  done 
in  the  first  one. 

From  the  last  kettle  on  the  left  side  the  lead  is  not 
further  concentrated,  but  laded  into  moulds  for  the  mar- 
ket. It  contains  from  one-fourth  to  one-half  ounce  of 
silver  per  ton.  The  enriched  lead  of  the  last  pot  has 
from  two  hundred  to  four  hundred  ounces  of  silver  per 
ton. 

The  following  scheme  gives  a  view  of  the  procedure 
of  the  work : 


248  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


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PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  249 

Extraction  of  Silver  from  Pig  Lead  with  Zinc. 

Sec.  73.  The  extraction  of  silver  from  argentiferous 
lead  with  zinc  is  executed  in  such  a  way  that  the  molten 
lead  is  stirred  with  fused  zinc  several  times,  whereupon, 
on  cooling,  argentiferous  zinc  is  eliminated  on  the  sur- 
face of  the  bath,  and  may  be  skimmed  with  a  perfora- 
ted ladle,  or  it  can  be  taken  up  in  the  shape  of  a  disk. 
The  zinc  is  then  parted  from  the  silver  by  acids  (muri- 
atic or  sulphuric  acid),  or  by  distillation.  The  silver  res- 
idue can  be  refined.  The  lead  must  be  refined  in  a 
reverberatory  furnace,  on  account  of  the  zinc  which  it 
retains.  The  desilverization  of  lead,  not  too  rich,  can  be 
accomplished  very  perfectly,  but  the  separation  of  lead 
from  zinc  is  imperfect.  For  this  reason,  and  because 
this  method  depends  on  the  price  not  only  of  the  zinc, 
but  also  on  that  of  chloride  or  sulphate  of  zinc,  this 
method  is  not  often  used. 

The  more  perfect  the  contact  between  lead  and  zinc 
is  effected,  the  more  complete  the  extraction  of  silver. 
Rich  lead  cannot  be  perfectly  desilvered  at  once.  A 
combination  of  Parke's  and  Pattinson's  methods  may 
answer  in  such  a  case.  The  first  extracts  the  greatest 
part  of  the  silver,  and  the  poor  lead  may  be  subjected  to 
the  crystallization  process,  purifying  it  at  the  same  time. 

Comparative  experiments  of  Parke's  and  Pattinson's 
methods  have  not  yet  been  made  sufficiently.  Accord- 
ing to  Nevil,  who  tried  both  methods,  Parke's  procedure 
yields  decidedly  more  silver.    According  to  his  state- 


250  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


ment,  the  loss  of  lead  was  one  per  cent,  and  of  the  zinc, 
three-fifths  of  the  quantity  of  zinc  alloyed  with  lead.  In 
the  establishment  of  Llanelly,  where  Pattinson's  process 
was  practiced  heretofore  in  twenty  pots,  they  have  been 
replaced  by  two  for  the  desilverization  with  zinc. 

The  quantity  of  zinc  depends  on  the  quantity  of  sil- 
ver in  the  lead,  and  also  on  the  amount  of  sulphur,  arse- 
nic, antimony,  etc.,  which  mostly  join  the  zinc. 

The  small  loss  in  metals,  which  occurs  in  this  process, 
recommends  it  for  poor  lead  which  could  not  be  desil- 
vered  otherwise  with  pecuniary  advantage.  At  Carmar- 
thenshire, in  South  Wales,  this  process  is  in  use,  and  has 
been  for  several  years.  The  operations  are  the  follow- 
ing: 

a.  Melting  of  Argentiferous  Lead  ivith  Zinc. — The  lead 
is  fused  in  a  large  iron  kettle,  holding  about  six  tons. 
When  this  is  done,  some  zinc  is  introduced  in  a  smaller 
handled  kettle,  and  heated  by  the  ascending  flame  from 
the  lead  kettle.  When  the  lead  and  zinc  are  fused,  the 
zinc  kettle  is  lifted  sideways,  and  the  contents  poured  in 
the  liquid  lead  at  once.  Lead  containing  fourteen  ounces 
of  silver  per  ton,  requires  one  per  cent,  of  zinc.  Four 
workmen  stir  the  mass  diligently  four  or  five  minutes, 
by  means  of  iron  curved  rods,  whereupon,  the  whole  is 
allowed  to  rest  five  minutes.  The  eliminated  scum  is 
skimmed  with  large  perforated  ladles,  made  of  sheet-iron. 

b.  Separation  of  Argentiferous  Zinc  from  adhering  Lead. — 
The  plumbiferous  zinc-scum  is  heated  slightly  in  a  fire- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  251 

proof  retort,  not  however  above  the  melting-point  of  the 
lead,  which  liquates  and  collects  in  a  basin,  while  the 
residue  is  drawn  out  at  the  rear  of  the  retort. 

c.  Distillation  of  Argentiferous  Zinc. — The  argentiferous 
zinc  is  placed  in  pots,  which  contain  three  openings. 
One  is  the  feed-hole,  which  is  closed  with  a  suitable 
brick  during  the  retorting.  On  the  bottom  is  another 
hole  by  which  the  residue  is  taken  out.  The  third  hole, 
on  the  side,  serves  for  the  escape  of  zinc-vapors.  These 
retorts  are  placed  over  a  grate  and  heated,  whereby  the 
zinc  distills  and  is  used  over  again  for  desilverization. 
The  residue  must  be  refined  with  a  small  addition  of 
lead. 

d.  Cleaning  of  the  Desilverized  Lead. — In  a  reverbera- 
tory  furnace  with  a  low  arch,  the  lead  is  heated  rapidly 
with  closed  doors  to  a  dark  red  heat,  whereupon  the  air 
is  allowed  to  enter  the  furnace  through  the  door.  The 
crust  which  arises  on  the  surface  of  the  lead  is  drawn 
off  from  time  to  time,  and  such  temperature  maintained 
as  to  promote  the  oxydation  of  zinc,  but  low  enough  to 
prevent  the  formation  of  much  oxyd  of  lead.  If  the 
surface  remains  bright  the  lead  is  laded  into  moulds, 
and  is  a  very  pure  article. 

REFINING  OF  SILVER. 

Sec.  74.  The  refining  is  a  continuation  of  cupellation 
by  which  all  impurities  of  the  silver  are  oxydized  and 


252  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

parted,  but  it  is  performed  generally  in  a  more  concen- 
trated space.  The  oxydation  process  is  carried  on  in 
the  cupelling  furnace  till  the  silver  brightens  ;  it  con- 
tains several  per  cent,  of  impurities  yet,  as  lead,  copper, 
antimony,  etc.  A  small  quantity  of  lead,  antimony,  or 
arsenic  makes  the  silver  brittle,  but  copper  does  not  in- 
jure its  ductility.  It  may,  therefore,  be  desirable  under 
certain  circumstances,  to  leave  the  copper  in  the  alloy. 

The  refining  is  very  simple,  if  the  impurity  consists 
only  of  lead ;  but  if  a  considerable  amount  of  copper, 
arsenic,  and  antimony,  and  less  lead  are  alloyed  with 
the  silver,  the  separation  of  those  substances  by  a  mere 
oxydizing-melting  takes  a  very  long  time  to  accomplish 
by  the  action  of  the  atmospheric  air.  Besides  this,  the 
silver  requires  more  heat  if  little  or  no  lead  is  in  it.  In 
such  cases,  it  is  advantageous  to  add  some  lead ;  it 
being  oxydized,  eliminates  also  the  other  impurities. 

According  to  Karsten,  to  one  part  of  foreign  sub- 
stances, eighteen  parts  of  lead  should  be  used.  In  case 
the  silver  contains  nickel  or  cobalt,  an  addition  of  some 
copper  is  advantageous.  The  formed  litharge  is  not 
drawn  out  of  the  furnace,  but  is  absorbed  by  the  porous 
mass  of  the  test  (marl  or  bone-ashes,  etc.). 

The  porous  mass  is  either  on  a  movable  hearth,  or  a 
fixed  one.  The  movable  one  is  an  iron  bowl  or  an  iron 
ring  prepared  with  porous  fire-proof  material.  These 
tests  are  placed  in  the  refining  furnace.  The  unmov- 
able  test  does  not  differ  much  from  a  cupelling  furnace 
except  in  smaller  dimensions,  which  are  relative.  The 


PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  253 

oxydation  is  effected  either  by  blast  or  draft.  The 
refined  silver  is  not  chemically  pure. 

The  sign  of  pure  silver  is  the  so-called  "  spitting  "  of 
the  silver.  When  the  surface  of  the  silver  begins  to 
harden  an  eruption  of  metal,  assuming  different  forms, 
takes  place ;  and  during  this  process  small  globules  are 
often  thrown  off.  This  phenomena  had  been  attributed 
to  a  physical  cause,  but  it  was  discovered  by  Lucas  that 
silver  possesses  the  remarkable  property  of  absorbing, 
while  in  melted  condition,  a  large  quantity  of  oxygen 
gas  (at  least  twenty-fold  volume  of  the  metal)  which 
absconds  rapidly  during  the  refrigeration  of  the  metal, 
forming  figures  one  or  two  inches  high,  whereby  some 
silver  is  often  scattered. 

By  a  very  slow  cooling  the  spitting  can  be  avoided. 
The  oxygen  can  be  ascertained  very  easily  by  throwing 
charcoal-dust  on  the  place  where  the  spitting  occurs.  A 
very  lively  burning  of  the  carbon  will  be  perceived. 
The  silver  absorbs  oxygen  from  saltpetre  if  covered 
with  it  when  molten,  but  when  the  contact  with  the  air 
is  interrupted  by  a  cover  like  common  salt,  no  spitting 
will  occur. 

A  small  amount  of  gold  does  not  impede  the  spitting, 
but  it  does  not  appear  if  some  lead  or  copper  is  alloyed 
with  silver. 

After  the  refining,  the  test-mass  or  hearth  is  found  to 
contain,  besides  some  metallic  and  oxydized  silver,  also 
the  oxyds  of  foreign  metals,  which  were  alloyed  with 
the  silver.    The  silver  in  such  hearths  may  sometimes 


254  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


amount  to  six  hundred  ounces  per  ton,  for  that  reason 
it  is  always  given  over  to  the  smelting  process. 
The  usual  methods  of  refining  are  the  following : 

A.  Refining  on  movable  hearths  or  tests. 

1.  Before  the  blast. 

2.  Under  the  muffle. 

3.  In  reverberatory  furnaces. 

B.  Refining  on  fixed  hearths  in  reverberatory  or 
draft  furnaces. 


Refining  in  small  draft  furnaces  is  the  most  advan- 
tageous and  simplest  method.  The  least  advisable  is 
the  refining  under  the  muffle,  which  consumes  the  most 
fuel,  but  in  regard  to  cleanness  and  proper  work  is 
preferable.  The  refining  before  the  blast  is  more  diffi- 
cult. 

A.    Refining  on  Movable  Tests. 

Refining  before  the  Blast. — In  regard  to  fuel,  this  mode 
is  economical  and  very  suitable  for  impure  silver,  which 
requires  a  powerful  oxydation,  especially  if  some  copper 
is  allowed  to  remain  in  the  silver.  It  needs  some  exer- 
cise to  conduct  the  process,  so  as  to  keep  the  silver 
always  at  a  proper  heat.  Using  the  blast,  the  silver  is 
disposed  to  volatilize. 

In  Freiberg,  this  procedure  is  practiced  in  such  a  man- 
ner that  the  silver  in  portions  of  from  three  hundred  and 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  255 

twenty  to  four  hundred  and  eighty  ounces  is  melted  be- 
fore the  blast  in  iron  tests,  which  are  lined  by  stamped 
marl.  These  tests  are  from  nine  to  eleven  inches  wide, 
and  about  three  inches  deep.  When  the  silver  is  intro- 
duced, some  live  coals  are  placed  before  the  tuyere,  and 
around  the  test  there  is  a  ring  of  sheet-iron  filled  with 
charcoal,  then  the  blast  is  thrown  in.  The  blast  yields 
about  eighteen  cubic  feet  of  air  per  minute.  When  the 
silver  is  molten,  the  ring  must  be  removed,  the  glowing 
coal  drawn  from  the  surface  of  the  silver,  and  the  heat 
maintained  by  placing  some  thin  pieces  of  wood  between 
the  silver  and  blast,  and  covering  the  wood  with  some 
live  coal,  so  that  only  the  flame  is  carried  over  the  sur- 
face of  the  silver.  Care  must  be  taken  not  to  let  the 
silver  refrigerate,  and  also  to  avoid  the  contact  of  coal 
and  metal.  The  process  is  continued  under  frequent 
stirring,  till  the  litharge  spots  cease  to  appear.  A  small 
iron  hook  is  then  dipped  into  the  silver  and  the  adher- 
ing drop  examined.  It  is  sufficiently  fine,  if  the  dark 
red-hot,  pear-shaped  drop,  appears  entirely  free  of  spots, 
spitting  on  cooling,  and  assuming  at  the  same  time  a 
perfect  white  color.  The  metal  in  the  test  is  perfectly 
lustrous.  The  blast  is  stopped,  the  silver  cooled  cau- 
tiously with  water,  then  taken  out  and  cleaned.  One 
trip  takes  from  one  to  one  and  a  half  hours,  consuming 
2*2  cubic  feet  of  charcoal,  and  1*1  cubic  feet  of  wood. 

Refining  under  the  Muffle. — This  method  consumes  more 
fuel  than  the  preceding,  but  it  is  cleaner,  easier,  and 


256  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

more  correct  work.  This  mode  is  more  suitable  for  a 
poorer  sort  of  silver. 

The  tests  are  of  about  the  same  size  and  prepared  in 
the  same  way  as  the  preceding  and  placed  in  a  corres- 
ponding hollow  place  of  the  furnace,  as  level  and  secure 
as  possible.  The  silver  is  then  introduced,  and  the  test 
covered  with  the  muffle.  The  whole  arrangement  is  in 
a  small,  vertical  furnace,  widened  in  the  middle,  with  an 
aperture  in  the  front.  On  the  periphery  at  the  bottom, 
are  six  little  draft-holes,  each  half  an  inch  square.  By 
these  holes  the  draft  is  regulated.  The  draft-holes  of 
the  muffle  must  be  carefully  covered  with  pieces  of  bro- 
ken muffles,  then  the  charcoal  in  large  pieces  introduced 
around  the  muffle.  The  aperture  is  closed  by  a  tile  with 
a  hole  in  it,  through  which  the  inside  of  the  muffle  can 
be  seen.  The  furnace  is  filled  with  charcoal  and  the  fire 
started. 

When  molten,  the  silver  must  be  stirred  often  by 
means  of  an  iron  hook,  and  the  process  continued  by 
closed  or  open  muffle,  as  the  temperature  may  require, 
till  no  forming  litharge  is  perceptible,  and  the  metal 
looks  perfectly  bright.  When  this  state  is  obtained,  the 
silver-cake  is  cooled  with  water.  The  metal  will  soon 
commence  to  spit.  An  iron  hook  is  pressed  into  the  sil- 
ver, on  the  spot  where  the  spitting  takes  place,  and  by 
means  of  it,  the  silver  cake  is  taken  out.  At  Oker  on 
the  Hartz,  eight  hundred  ounces  of  the  introduced  silver 
yields  seven  hundred  and  sixty  ounces  fine  silver  in  five 
hours. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  257 

Procedure  of  the  Mint  at  Clausthal. — The  iron  test-bowl 
is  filled  with  wood  ashes,  well  lixiviated,  and  beaten  in 
level  with  the  edge,  whereupon  a  cavity  is  cut  out  about 
twelve  inches  in  diameter,  and  from  three  to  four  inches 
deep.  There  are  three  furnaces  of  the  preceding  des- 
cription, each  for  one  muffle,  and  two  larger  ones,  in 
each  of  which  four  muffles  are  placed.  The  latter  fur- 
naces are  provided  with  four  draft-holes  on  the  back 
wall.  The  smaller  ones  have  holes  on  two  sides,  and 
one  behind.  The  tests  are  placed  in  the  furnace  as 
above  described,  charged  with  seven  hundred  ounces, 
and  by  closed  muffle,  melted  down  in  about  two  hours. 
After  this  the  muffle  is  opened  and  the  metal  stirred  for 
some  time  with  an  iron  hook,  then  shut  up  for  half  an 
hour,  and  then  stirred  again.  This  is  repeated  three 
times  at  intervals  of  half  hours,  whereupon  the  last  heat 
is  given,  half  an  hour  long.  During  the  stirring,  lith- 
arge eyes  are  produced  on  the  surface  of  the  bath.  At 
the  end  of  the  operation  they  disappear.  As  soon  as  the 
silver  looks  perfectly  bright,  it  is  cooled  by  pouring  wa- 
ter on  it.  The  spitting  is  impeded  by  keeping  an  open 
hole  in  the  centre  of  the  cake  with  an  iron  hook. 

B.    Refining  in  Reverberatory  Furnaces. 

The  reverberatory,  or  flame  furnaces,  have  movable 
or  fixed  hearths,  and  are  covered  with  an  arch  or  mova- 
ble cap.  They  do  not  differ  much  from  the  cupelling 
furnaces,  save  the  size.  The  heat  is  produced  by  wood, 
coal,  or  gas. 

17 


258  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

The  test-rings,  or  brick  hearths,  are  prepared  either 
with  lixiviated  wood  ashes,  or  with  fine,  sifted  marl. 
The  properly  cut  and  dried  test  is  placed  in  the  furnace, 
the  silver  introduced,  covered  with  small  charcoal,  and 
heated  to  nearly  white  heat  at  well  closed  doors.  To 
avoid  losses  of  silver,  it  is  a  principal  rule  to  cover  it 
with  fine  charcoal  or  saw-dust,  and  to  melt  it  down 
quickly,  and  to  refine  it  at  a  lower  temperature.  The 
silver  volatilizes  at  the  beginning  of  the  white  heat, 
especially  under  draft;  this  must  be  kept  from  the  sil- 
ver by  the  cover  of  charcoal.  The  more  antimony, 
arsenic,  or  lead,  the  silver  contains,  the  easier  it  volatil- 
izes, requiring  the  charcoal  cover  to  be  kept  on  it  so 
much  longer.  When  molten,  and  no  more  silver  is  add- 
ed, the  slag  is  drawn  off,  the  metal  stirred,  and  the  sur- 
face cleaned.  The  temperature  is  so  conducted,  that  the 
eyes,  swimming  on  the  surface,  should  not  glide  too  fast 
towards  the  sides.  At  a  too  high  temperature,  the  sil- 
ver assumes  a  vibrating  motion,  many  pearls  hasten 
from  the  middle  towards  the  periphery,  and  the  silver 
does  not  adhere  to  an  iron  rod,  if  quickly  dipped  in  and 
withdrawn.  The  temperature  is  too  low,  when  on  the 
edge  of  the  silver  bath  commencing  refrigeration  be 
observed. 

If  the  fusion  is  not  easily  obtained,  some  lead,  from 
four  to  six  per  cent.,  may  be  added.  Easy  refrigerating 
and  slow  refining  silver  requires  some  copper.  If,  after 
some  stirring,  a  bright  surface  is  observed,  the  assay 
must  be  taken,  by  dipping  a  curved  iron  rod  about  half 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  259 

an  inch  deep  into  the  silver  till  the  latter  assumes  a 
pear-like  shape.  It  is  pure  if  no  spots  of  litharge  or 
oxyd  of  copper  are  perceived  on  it,  and  if  the  silver 
runs  off,  or  endeavors  to  drop  off,  when  dipped  again. 
In  the  reverse  case,  the  refining  must  continue.  When 
fine,  the  silver  is  cooled  with  water  and  removed.  In 
Freiberg,  the  refining  furnace  is  charged  at  once  with 
from  twelve  hundred  to  thirteen  hundred  pounds  of 
silver. 

Refining  in  Crucibles. 

Generally  only  the  purer  silver  is  subjected  to  refin- 
ing in  crucibles.  The  melting  is  performed  either  in  a 
black-lead  or  cast-iron  crucible,  either  with  charcoal  or 
with  the  flame  of  coal,  in  reverberatory  furnaces,  in 
which  the  crucible  is  placed.  The  black-lead  crucibles 
at  Freiberg  have  been  replaced  by  cast-iron  ones  in 
flame -furnaces,  offering  many  advantages  over  the  for- 
mer in  draft  furnaces,  with  charcoal. 

The  loss  of  silver  by  volatilization  was  brought  down 
to  the  minimum,  while,  when  exposed  to  the  strong 
draft  of  the  crucible  furnace  in  a  black-lead  crucible,  it 
was  considerable.  The  use  of  coal  proved  more  econom- 
ical than  charcoal,  and  the  iron  crucibles  stood  longer 
than  the  black-lead  crucibles.  At  a  white  heat  in  an 
uncovered  crucible  the  silver  loses  about  one  per  cent, 
per  hour. 

At  Przibram  (Bohemia)  the  crucible  is  charged  by 
degrees,  with  from  4,800  to  9,600  ounces  of  silver,  and 


260  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

melted  in  five  or  six  hours.  A  mixture  of  two  parts 
lixiviated  ashes,  and  one  part  bone-ashes,  is  introduced 
on  the  molten  silver,  by  means  of  an  iron  ladle,  stirred 
in  such  a  way  on  two  places,  as  to  obtain  two  openings 
in  the  mass,  through  which  the  oxygen  of  the  air  cj 
come  into  contact  with  the  silver.  The  oxyd  of  lead  is 
taken  up  by  the  porous  mass,  and  this  removed  by 
means  of  a  ladle.  This  operation  must  be  repeated  at 
gradually  longer  intervals,  till  the  silver  commences  to 
boil  and  to  show  a  bright  surface.  After  this,  a  mixture 
of  one  ounce  and  a  half  of  borax  with  the  same  quantity 
of  saltpetre,  is  introduced,  and  then  the  slag  skimmed 
off,  after  a  quarter  of  an  hour's  time.  The  silver  is  im- 
mediately covered  with  charcoal  dust  and  a  good  heat 
applied  for  a  quarter  of  an  hour,  when  the  silver  is  dip- 
ped into  moulds.  This  method  suffers  a  small  loss  * 
silver,  consuming  comparatively  very  little  fuel,  but  th 
operation  requires  more  time. 


CHAPTER  IV. 


EXTRACTION  OF  SILVER  IN  THE  WET  WAY. 

A.    EXTRACTION  BY  QUICKSILVER  OR  AMALGAMA- 
TION. 

Sec.  75.  Where  gold  and  silver  ores  were  found  in 
large  quantities,  but  no  fuel,  it  was  necessary  to  search 
for  other  means  of  reduction  than  heat,  and  this  was 
found  in  quicksilver.  Poor  silver  ores,  containing  small 
quantities  of  lead,  are  also  suitable  for  amalgamation. 

The  extraction  of  silver  by  quicksilver  is  founded  on 
the  property  of  the  latter  to  form  an  alloy  with  the 
silver,  which  can  be  separated  by  heat.  A  procedure 
for  extracting  the  silver  from  ores  by  quicksilver  was 
first  published  by  Bartolome  de  Medina  in  Mexico,  in 
the  middle  of  the  sixteenth  century.  In  the  year  1784 
the  amalgamation  was  introduced  in  Europe  first  by 
Born,  at  Vienna,  in  copper  kettles,  then  by  Gellert  in 
tubs,  and  finally  by  Ruprecht,  in  barrels. 

The  amalgamation,  compared  with  melting,  has  the 
advantage  of  saving  fuel,  rendering  the  silver  in  a  short 
time, — unlike  the  melting  by  which  the  silver  is  carried 


662  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

through  many  intermediate  products,  causing  thus  more 
loss  in  silver,  expense  of  time  and  money.  There  are 
chiefly  three  modes  of  amalgamation  : 

1.  European  Barrel-Amalgamation. 

2.  American  Amalgamation. 

a.  Heap- Amalgamation  (Patio). 

b.  Kettle- Amalgamation. 

3.  Combined  European  and  American  method. 

European  Barrel  Amalgamation. 

The  European  barrel-amalgamation  is  more  perfect 
than  the  patio-amalgamation,  yielding  the  silver  in 
much  shorter  time  and  with  less  quicksilver  consume, 
but  makes  the  use  of  more  machinery  and  fuel  neces- 
sary. In  both  methods  the  silver  must  be  converted 
into  a  chloride  and  decomposed  in  the  barrels  by  iron, 
in  the  patio  by  quicksilver.  The  European  method  is 
applied  to  ores,  matts,  and  black  copper. 

Amalgamation  of  Silver  ores. 

All  silver  ores  are  not  suitable  for  amalgamation. 
Copper,  lead,  antimony,  arsenic,  and  zinc,  are  not  agree- 
able customers,  partly  because  they  enter  the  amalgam, 
and  because  they  effect  losses  of  silver  and  quicksilver 
by  volatilization,  also  impede  the  amalgamation  and 
produce  richer  tailings  (the  last  is  caused  by  lead).  The 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  263 

zincblend  needs  a  strong  heat,  but  decomposes  the  salt 
very  little.  Argentiferous  blend  loses  a  great  deal  of 
silver  by  volatilization. 

Iron  acts  favorably ;  manganese,  nickel,  and  cobalt  are 
not  injurious.  Experience  shows  that,  concerning  earthy 
matters,  quartzose  ores  yield  more  silver  but  less  pure 
amalgam,  and  cause  larger  loss  in  quicksilver,  while 
calcareous  ores  work  better  on  quicksilver,  giving  also 
purer  amalgam,  but  less  silver.  The  best  economical 
result  is  obtained  by  mixing  both  kinds.  Clayish  ores 
are  amalgamated  with  difficulty. 

The  ores  best  suitable  are  the  pyritous,  sulphuretted 
silver  ores,  without  regard  to  richness,  but  salt  and 
quicksilver  must  be  regulated  according  to  the  richness. 
In  roasting  the  ore  with  salt,  a  certain  amount  of  pyrites 
is  necessary  for  the  formation  of  chlorine,  which  is  ascer- 
tained by  an  assay  for  matt.  If  there  is  no  pyrites  in 
the  ore,  iron  or  magnetic  pyrites,  matt  or  green  vitriol, 
must  be  added. 

The  Roasting — With  the  intention  of  forming  chloride 
of  silver — is  one  of  the  most  important  preparations  of 
the  ore.  It  must  be  executed  with  great  care.  In 
Freiberg,  one  charge  used  to  be  four  hundred  and  fifty 
pounds.  It  is  introduced  into  the  dark  red  furnace, 
carefully  spread  on  the  hearth,  stirred  and  the  lumps 
broken  with  a  long-handled  hammar.  After  this,  a 
moderate  fire  is  started  and  continued,  gradually  raising 
the  heat  for  about  two  hours.  At  this  time,  the  furnace 
having  assumed  a  light  red  heat,  the  sulphur  begins 


264  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


to  burn.  In  the  first  period,  white  vapors  arise  chiefly 
of  water,  antimony,  arsenic,  and  zinc. 

With  the  beginning  of  the  burning  of  sulphur  or 
desulphurization,  the  second  period  commences.  Under 
constant  stirring  the  fire  must  be  made  to  go  down,  as 
the  burning  sulphur  creates  a  sufficient  temperature.  In 
this  period,  lasting  again  two  hours,  the  principal  action 
on  the  ore  is  effected  in  an  oxydizing  manner  by  the 
atmospheric  air.  Sulphurous  acid,  basic,  and  neutral 
sulphates  are  formed,  as  well  as  free  oxyds ;  but  some 
sulphides  remain  also  undecomposed,  resulting  from 
higher  sulphur  combinations. 

When  the  odor  of  sulphurous  acid  has  disappeared, 
and  the  temperature  has  sunk  to  dark  red  heat,  the  last 
period  begins.  The  heat  must  now  be  raised,  under 
continual  stirring;  the  ore  swells  up,  enlarging  its 
volume,  greenish-gray  vapors  are  emitted,  and  the  last 
period  is  generally  finished  in  three-quarters  of  an  hour, 
and  the  ore  drawn  out  while  the  evolution  of  gases  is 
still  going  on. 

The  sulphates,  especially  the  sulphate  of  iron,  act  in 
this  period  on  the  salt,  whereby  partly  free  chlorine 
and  partly  hydrochloric  gas  is  formed,  the  latter  in  the 
presence  of  water-vapors  which  are  always  supplied  by 
the  fuel  and  air.  In  passing  through  the  ore,  the  chlo- 
rine decomposes  principally  the  sulphides  which  escaped 
decomposition  by  heat,  forming  volatile  chlorides  of 
sulphur,  arsenic,  antimony,  iron,  and  zinc,  also  un vola- 
tile chlorides  of  gold,  silver,  copper,  lead,  nickel,  cobalt, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  265 


iron,  and  manganese.  The  hydrochloric  gas  changes 
principally  the  oxydated  metal  combinations  into  chlo- 
rides. The  chlorination  of  silver  already  begins  in  the 
second  period  of  roasting,  but  principally  in  the  third. 
If  the  roasting  was  well  performed,  all  silver  must  be 
changed  into  a  chloride,  otherwise  some  sulphurets  of 
silver  remain  undecomposed  and  the  tailings  become 
rich. 

Examining  the  ore  during  the  roasting  for  chloride 
of  silver,  the  following  procedure  will  show  the  result: 

A  sample  is  taken  from  the  furnace  and  one  ounce  of 
it  weighed  out,  introduced  into  a  filter  and  lixiviated 
with  a  hot  solution  of  salt  until  a  clean  piece  of  copper 
does  not  show  a  white  coating  of  precipitated  silver. 
The  ore  is  then  dried  and  assayed  for  silver. 

The  roasted  ore  must  be  sifted  and  ground.  The 
coarse  part  is  ground  separately  and  roasted  over  with 
two  per  cent,  of  salt ;  the  fine-sifted  and  ground  ore  is 
given  over  to  the  amalgamation. 

Amalgamation. — This  is  performed  in  barrels  made  of 
oak  or  pine  wood.  The  first  period  is  the  preparation 
of  the  pulp.  For  this  purpose  water  (three  hundred 
pounds)  is  led  into  each  barrel  and  1,000  pounds  of 
roasted  ore  introduced,  also  one  hundred  pounds  of 
wrought-iron.  The  barrels  are  shut  and  started  with  a 
speed  of  fourteen  to  sixteen  revolutions  per  minute.  ■ 
The  water  dissolves  all  soluble  salts  and  exposes  in  this 
way  the  particles  of  chloride  of  silver.  In  this  period 
the  iron  acts  decomposingly  on  the  chlorides  of  iron  and 


266  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

copper,  changing  them  into  sub-chlorides  which  are  not 
injurious  to  the  quicksilver.  The  chlorides  of  copper 
and  iron  would  transform  a  part  of  the  quicksilver  into 
sub-chloride  which  would  be  lost  in  the  tailings.  The 
dissolved  chlorides  of  silver,  gold,  and  copper  are  re- 
duced by  the  iron  to  a  metallic  state.  After  two  hours' 
preparatory  run,  during  which  the  pulp  has  obtained 
the  proper  consistency,  the  barrels  must  be  arrested 
and  the  second  period  (the  amalgamation)  commences. 
To  each  barrel  is  now  added  five  hundred  pounds  of 
quicksilver.  When  secured,  the  barrels  are  started 
again  for  twenty  hours  with  a  speed  of  twenty  to 
twenty-two  revolutions  per  minute.  By  a  galvanic 
action  the  further  decomposition  of  the  chloride  of 
silver  takes  place.  The  galvanic  action  is  created  by 
the  positive  iron,  the  negative  quicksilver,  and  the  dis- 
solved salts  as  conductor.  The  negative  chlorine  com- 
bines with  the  iron,  the  positive  silver  with  the  negative 
quicksilver.  Temperature  is  produced  by  these  actions. 
Besides  the  chloride  of  silver,  also  other  metal  combina- 
tions are  decomposed  by  the  galvanic  action,  especially 
copper,  lead,  antimony,  and  gold,  which  combine  with 
the  quicksilver. 

The  third  period  is  the  separation  of  amalgam  and 
residue.  The  amalgam,  disseminated  in  the  pulp  is 
separated  by  water,  with  which  the  arrested  barrels  are 
charged  over  two-thirds  full,  and  again  brought  in  mo- 
tion for  two  hours,  revolving  eight  or  nine  times  per 
minute,  whereupon  the  amalgam  and  quicksilver  is  dis- 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  267 

charged,  first,  through  a  small  hole  in  the  ping,  then 
the  residue  through  a  large  hole  (five  to  six  inches 
in  diameter). 

The  residue  of  each  five  barrels  runs  into  one  agita- 
tor, in  which  the  amalgam  still  left  settles  to  the  bottom, 
while  the  tailings  are  discharged  gradually  through 
three  holes,  one  above  the  other. 

The  amalgam,  when  discharged  from  the  barrel  is  led 
directly  into  canvass  filters.  The  quicksilver,  pressed 
by  its  own  weight,  runs  through  the  cloth  into  a  reser- 
voir. 

If  it  ceases  to  run,  the  separation  of  the  remainder  of 
the  quicksilver  is  performed  by  pressing  with  the  hands 
or  press. 

Amalgamation  of  Copber-Matt. 

The  copper-matt  amalgamation  makes  the  same  man- 
ipulation necessary  as  the  working  of  ores.  The  matt, 
however,  after  a  first  raw  roasting  is  drawn  out,  mixed 
with  salt  and  lime,  moistened,  and  the  mass  after  proper 
drying,  roasted  again.  This  modification  is  based  on 
the  amount  of  copper  in  the  matt,  with  the  object  of 
changing  the  chloride  of  copper  into  oxyd  of  copper, 
because  the  chloride  of  copper  chloridizes  a  part  of 
the  quicksilver  when  in  contact.  In  the  first  roasting 
of  the  matt,  sulphates  of  copper,  silver,  and  iron  are 
formed.  By  the  action  of  salt,  they  are  transformed 
into  the  chlorides  of  copper,  and  silver,  and  sequi-chlo- 
ride  of  iron.     The  lime  decomposes  the  chloride  of 


268  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

copper  and  sesqui-chloride  of  iron  into  hydrated  oxyds, 
without  changing  the  chloride  of  silver.  Herein  the 
experience  that  an  addition  of  lime  diminishes  the  loss 
of  quicksilver  is^  accounted  for.  The  subsequent  or  the 
second  roasting  is  performed  at  a  higher  temperature, 
effecting  the  perfect  chlorination  of  the  silver. 

The  amalgamation  of  the  matt  is  advantageous,  if 
there  is  no  gold  in  the  ore,  no  lead  ore  to  be  had  or  the 
fuel  is  scarce,  otherwise  melting  with  lead  would  be 
preferable. 

Amalgamation  of  Argentiferous  Arsenides  (Speiss)  ob- 
tained in  Melting. 

The  arsenides,  obtained  in  melting  of  cobalt  ores,  are 
analogous  to  the  matts.  In  the  first  place  we  have 
arsenic,  in  the  second  sulphur  combined  with  metals. 
The  amalgamation  of  Speiss  is  executed  in  Saxony.  It 
requires  a  very  careful  roasting  and  fine  grinding,  and 
an  addition  of  sufficient  salt.  As  there  is  not  sufficient 
sulphur  in  the  ore,  by  which  the  salt  can  be  decom- 
posed, two  and  a  half  or  three  per  cent,  of  green  vitriol 
must  be  added  for  that  purpose.  The  tailings  contain 
five  ounces  of  silver  to  the  ton,  but  the  average  loss  is 
about  thirteen  per  cent. 

Amalgamation  of  Argentiferous  Black  Copper. 

Experience  proves  that  the  alloy  of  silver  and  copper, 
without  sulphur,  decomposes  the  salt  forming  chlorides 
of  silver  and  copper.    The  closer  the  contact  between 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  269 

salt  and  copper,  the  more  chloride  of  silver  is  formed. 
The  chloride  of  copper  transfers  also  chlorine  to  the 
silver,  being  thus  reduced  to  sub-chloride. 

Black  copper  requires,  as  well  as  the  ores,  an  abund- 
ance of  salt,  and  deserves  preference  to  the  copper-matt 
amalgamation  on  account  of  its  simplicity  and  more 
perfect  extraction  of  silver.  This  method  has  a  decided 
advantage  over  the  liquation  process,  on  black  copper, 
free  from  lead  and  gold. 

In  Schmolnitz  (Hungary)  the  black  copper  contains 
from  one  hundred  and  ten  to  one  hundred  and  fifty 
ounces  of  silver  per  ton,  and  eighty-five-eighty-nine 
per  cent,  of  copper.  This  copper  is  heated  red  in  a 
reverberatory  furnace  and  stamped  in  glowing  condi- 
tion, then  sifted  and  ground  to  fine  powder.  For  the 
roasting,  four  hundred  pounds  is  taken  to  each  charge 
and  oxyd  with  seven  to  nine  per  cent,  of  common  salt. 
After  roasting,  it  is  ground  again,  and  then  amalgam- 
ated. The  barrels  are  charged  with  from  1,200  to  1,500 
pounds  each,  one  hundred  pounds  of  copper  balls,  four 
hundred  pounds  of  quicksilver,  and  the  required  quan- 
tity of  water.  The  loss  of  silver  is  four  and  three- 
fourths  per  cent.,  of  which  only  two  and  a  half  per  cent, 
remains  in  the  residue.  The  pure  copper  resulting  from 
this  process  contains  about  ten  ounces  of  silver  to  the 
ton.  At  Tajova,  a  loss  of  twenty-seven  per  cent,  of 
silver  occurs  and  the  copper  retains  twenty  ounces  per 
ton. 

At  Offenbanya  (Transilvania)  the  black  copper  con- 


270  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 


tains  some  lead,  and  on  this  account  three  per  cent,  of 
saltpetre  is  added  with  the  salt  in  roasting. 


B.    EXTRACTION  OF  SILVER  BY  DISSOLUTION  AND 
PRECIPITATION. 

Augustin's  Extraction  with  Solution  of  Salt. 

Sec.  76.  This  method  is  based  on  the  solubility  of 
the  chloride  of  silver  in  concentrated  solution  of  com- 
mon salt,  from  which  it  is  precipitated  by  copper.  If 
water  is  added  to  a  salt  solution  with  dissolved  chloride 
of  silver,  the  latter  will  be  again  separated  in  form  of 
chloride  of  silver  as  a  white  precipitate.  This  fact,  on 
which  Augustin  based  his  extracting  method,  has  been 
known  a  long  time.  It  was  first  executed  on  copper- 
matt  at  Gottes-belohnung  works,  and  since  then  at  other 
places,  also  on  other  argentiferous  products  and  ores. 
The  best  results  have  been  obtained  on  copper-matts. 

Extraction  of  Silver  from  Copper-Matt. 

The  Copper- Matt — Suitable  for  extraction  must  be  as 
rich  in  copper  as  possible,  otherwise  the  residue  becomes 
too  rich  in  silver.  Poorer  copper-matts  are  therefore 
concentrated  by  melting  in  reverberatory  furnaces,  being 
thus  enriched  to  from  sixty  to  seventy  per  cent.  The 
matt  must  be  free  from  or  should  contain  very  little 
lead,  antimony,  zinc,  or  arsenic,  or  else  a  considerable 
loss  in  silver  might  occur. 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  271 

Lead — Makes  the  roasting  troublesome,  having  an 
inclination  to  melt,  which  counteracts  the  formation  of 
the  chloride  of  silver.  At  the  same  time  chloride  of 
lead  is  created,  which  would  also  be  dissolved  in  the 
salt  solution,  causing  an  impure  precipitation  of  silver. 
Sulphuret  of  zinc,  to  a  certain  amount,  is  injurious  in 
a  chloridizing  roasting,  because,  when  changed  into  a 
sulphate,  it  requires  a  high  temperature  to  drive  the 
sulphuric  acid  out,  which  must  be  done,  otherwise  too 
much  chloride  of  zinc  will  be  formed.  But  at  a  high 
temperature  the  matt  softens  by  commencing  to  melt, 
causing  thus  richer  tailings  and  also  a  larger  loss  of 
silver  by  volatilization.  For  this  reason,  zinciferous 
matt  must  be  freed  from  zinc  by  concentration-smelting 
in  reverberatory  furnaces. 

Antimony  and  Arsenic,  in  a  chloridizing  roasting,  pro- 
duce also  antimonate  and  arsenate  of  silver,  neither  of 
which  can  be  decomposed  by  the  chlorine.  Introduced 
steam,  however,  forms  hydrochloric  acid,  by  which  the 
above  combinations  are  decomposed,  resulting  in  chlo- 
ride of  silver  and  volatile  chlorides  of  antimony  and 
arsenic. 

The  fine  pulverized  matt,  principally  consisting  of 
sulphides  of  iron,  copper,  and  silver,  is  first  roasted 
without  salt,  whereby  the  iron  is  converted  into  sul- 
phate of  iron,  then  sulphate  of  copper  is  formed,  and 
finally  sulphate  of  silver.  The  temperature,  under 
which  the  sulphate  of  silver  is  produced,  is  so  high 
that  almost  all  the  sulphate  of  iron  and  a  great  part  of 


272  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  sulphate  of  copper  will  be  decomposed,  so  that  at 
the  end  of  roasting  the  mass  consists  chiefly  of  the 
oxyds  of  iron  and  copper,  some  sulphate  of  copper  and 
sulphate  of  silver,  as  well  as  some  undecomposed  sul- 
phides. From  time  to  time  samples  are  taken,  to  ascer- 
tain the  condition  of  the  roasting.  The  sample  is  placed 
on  a  filtering  paper  and  lixiviated  with  water.  The 
blue  color,  according  to  its  intensity,  shows  the  pres- 
ence of  more  or  less  sulphate  of  copper.  An  addition 
of  salt  solution  gives  a  white  precipitate  of  chloride  of 
silver. 

In  the  second  roasting  period  the  oxydation  is  con- 
tinued for  a  while  at  an  increased  heat,  in  order  to 
decompose  all  sulphides  of  iron,  copper,  and  silver. 
When  a  sample,  taken  from  the  furnace  gives  a  feeble 
blue-colored  water,  and  with  salt  solution  a  strong  pre- 
cipitate of  silver,  the  purpose  of  the  oxydizing  roasting 
is  accomplished.  Now  is  the  time  to  introduce  the  salt 
and  to  change  the  roasting  into  a  chloridizing  one. 

The  sulphuric  acid,  which  is  principally  combined 
with  silver  and  to  some  extent  with  copper,  expells 
the  chlorine  of  the  salt,  forming  sulphate  of  soda  and 
sulphurous  acid.  The  chlorine,  penetrating  the  mass, 
creates  chloride  of  silver;  but  as  there  is  always  a  super- 
abundance of  chlorine,  it  creates  also  some  chloride  of 
copper  and  iron.  In  this  condition  the  roasted  matt  is 
subjected  to  lixiviation  with  hot  concentrated  solution 
of  salt.  The  desilverization  is  promoted  and  perfected  if 
the  solution  acts  under  pressure  upon  the  matt.  From 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  273 

the  solution,  the  silver  is  precipitated  by  metallic  cop- 
per. The  copper  precipitating  the  silver,  enters  into 
solution  and  is  precipitated  by  the  iron.  The  sub- 
chloride  of  copper  is  produced  by  decomposition  of 
chloride  of  silver,  and  also  by  decomposition  of  the 
chloride  of  copper  in  the  solution,  with  metallic  copper. 
The  products  of  this  process  are : 

1.  Cement-silver. 

2.  Cement-copper. 

3.  Residue  melted  for  copper. 

4.  Green  vitriol  or  sulphate  of  iron,  and, 

5.  Glauber's  salts. 

In  Freiberg  this  method  offered  also  a  great  advan- 
tage over  the  liquation  process,  and  is  executed  in  the 
following  way : 

The"  matt,  after  stamping  and  sifting,  is  subjected 
to  roasting  in  portions  of  from  three  hundred  to  four 
hundred  pounds.  The  roasting  is  performed  in  a  double 
furnace,  one  hearth  above  the  other.  Each  charge 
remains  four  hours  on  the  upper  and  four  hours  on  the 
lower  hearth.  The  roasted  matt  is  then  ground  fine, 
and  roasted  over  on  the  lower  hearth  for  one  hour  with 
an  addition  of  five  per  cent,  of  salt. 

The  roasted  matt  in  now  subjected  to  the  lixiviation. 
For  this  purpose  it  is  elevated  to  the  upper  story,  where 
18 


274  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  lixiviating  tubs  are  arranged.  They  are  three  feet 
nine  inches  high,  two  feet  eight  inches  in  the  upper 
and  two  feet  four  inches  in  the  lower  diameter,  and  are 
filled  with  from  four  to  six  hundred  pounds  of  matt. 
Each  of  these  tubs  has  a  filtering  apparatus  on  the 
bottom ;  first  a  wooden  cross  then  a  perforated  wooden 
bottom,  then  a  layer  of  straw  and  over  this  a  piece  of 
cloth,  made  tight  against  the  staves  of  the  tub,  by  being 
stretched  upon  a  hoop.  On  the  top  of  the  tub,  when 
filled  with  matt,  there  is  placed  a  perforated  wooden 
disk.  The  concentrated  hot  salt  solution  is  conveyed  in 
a  trough  to  the  tubs,  into  which  it  drops,  coming  out 
through  the  cock  at  the  bottom  saturated  with  the  chlo- 
ride of  silver.  This  cock  is  first  opened  for  the  escape 
of  vapor,  then  shut  for  a  quarter  of  an  hour  and  opened 
again,  taking  care  that  as  much  salt  solution  flows  into 
the  tub  as  comes  out  through  the  cock. 

The  lixiviation  is  performed  in  three  periods.  The 
first,  with  concentrated  solution,  takes  ten  hours.  The 
second,  also  with  concentrated  solution,  continues  till  a 
piece  of  clean  copper  does  not  become  coated  white; 
and  this  may  require  ten  or  twelve  hours  longer.  The 
last  lixiviation  is  done  with  clear  water.  The  products 
obtained  are : 

1.  Residue. — The  tubs  are  transported  on  a  railtrack 
to  a  discharge  place,  an  assay  is  taken,  and  in  case  the 
tailings  should  prove  to  be  unsufficiently  desilvered, 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  275 

they  must  be  roasted  over  again  with  salt.  They  con- 
tain from  forty  to  sixty-five  per  cent,  of  copper. 

2.  Silver  Salt  Solution — Which  is  conveyed  into  pre- 
cipitation tubs. 

3.  Lixiviating  Water. — This  water,  obtained  from  the 
third  period,  contains  salt.  It  is  led  into  a  basin  and 
used  again  for  lixiviation. 

The  cement-copper,  obtained  by  precipitation  with 
iron,  is  introduced  into  the  precipitating  tubs,  about  six 
inches  deep,  in  which  the  silver-containing  solution  is 
conveyed.  The  tub  is  provided  with  a  filtrating  appa- 
ratus, through  which  the  desilvered  solution  is  carried 
into  other  tubs  where  the  copper  is  precipitated  by 
iron  and  used  again  for  precipitating  the  silver. 

The  precipitated  silver  is  removed  at  intervals  of 
eight  days  from  the  copper  on  which  it  accumulates. 
Sub-chloride  of  copper  and  chloride  of  lead  are  separ- 
ated from  the  precipitated  silver  by  washing  it  with 
water  and  diluted  muriatic  acid,  then  melted  and  re- 
fined in  crucibles. 

C.    ZIERVOGEL'S  EXTRACTION  OF  SILVER  WITH 
WARM  WATER. 

Sec.  77.  Ziervogel's  method  of  silver  extraction  from 
matts  is  more  simple  and  cheaper  than  the  preceding. 
No  salt  is  used  here. 


276  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

In  roasting  pure  argentiferous  copper-matt  sulphate 
of  iron  is  first  formed,  then  sulphate  of  copper,  and 
finally  sulphate  of  silver.  The  formation  of  the  last 
sulphate  requires  such  high  temperature  that  it  decom- 
poses again  the  first  two  sulphates,  created  at  a  lower 
heat.  The  sulphates  of  iron  and  copper  are  decomposed 
into  oxyds,  and  sulphuric  acid  which  escapes,  while  the 
sulphate  of  silver  remains  undecomposed.  This  sul- 
phate is  soluble  in  hot  water,  and  can  be  precipitated 
by  copper. 

It  has  been  observed  generally  that  Ziervogel's 
method  is  simpler  and  cheaper,  and  the  lixiviation  is 
effected  quicker,  but  the  roasting  process  is  a  great  deal 
more  difficult,  purer  matts  are  necessary,  and  the  tailings 
are  richer  than  from  Augustin's  process. 

The  matt  is  pulverized  to  a  fine  powder,  and,  in 
charges  of  five  hundred  and  seventy-five  pounds,  roast- 
ed. There  are  double  furnaces  used  for  this  roasting. 
The  upper  floor  is  charged  with  the  matt,  and  this  stir- 
red for  one  hour  and  a  quarter ;  the  lumps,  if  any,  are 
mashed  and  the  mass  changed  so  that  the  cooler  part  is 
brought  nearer  to  the  fire,  and  vice  versa.  The  stirring 
is  continued  for  one  hour  and  a  half,  the  mass  changed 
again,  and  now  from  twenty  to  twenty-five  pounds  of 
coal-dust  are  added,  well  mixed,  for  ten  minutes  and 
then  conveyed  to  the  lower  hearth,  through  a  flue 
which  was  covered  with  an  iron  plate.  The  matt  is  now 
spread  on  the  red-hot  hearth,  and  stirred  for  about  one 
hour  and  a  quarter  without  using  any  fuel.    The  mass 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  277 

will  first  ignite  on  account  of  the  coal  dust.  It  is  then 
raked  together  and  the  different  heated  parts  change 
places.  A  sample  is  taken  from  the  bridge-side  with  an 
iron  ladle,  emptied  into  a  porcelain  cup,  so  as  to  divide  it 
in  two  partitions.  Cold  water  is  then  slowly  introduced 
on  one  side  till  it  penetrates  the  sample  and  comes  forth 
on  the  other.  The  water  must  appear  feebly-blue  color- 
ed, and  several  grains  of 'salt  must  not  produce  a  darker 
hue  but  precipitate  the  silver  as  a  white  substance. 

If  such  reaction  is  observed  the  matt  must  be  shift- 
ed, firing  and  stirring  continues  ;  another  sample  is 
taken  at  the  bridge-side  and  examined  in  the  same  way 
till  a  corresponding  result  is  obtained.  But  if  the  water 
should  show  a  green  color  from  sulphate  of  iron,  or  a 
deep  blue  from  sulphate  of  copper,  the  stirring  must  be 
continued. 

As  soon  as  the  roasting  is  finished  which  is  indicated 
by  the  above  sample,  a  sign  is  given  to  the  upper  work- 
man to  add  coal-dust  to  the  matt  of  the  upper  hearth. 
The  roasted  matt  from  the  lower  floor  is  removed  and 
sifted  through  a  sieve  of  sixteen  holes  to  the  square 
inch.  The  coarse  part  of  the  sifting  is  added  to  each 
charge  in  quantities  of  twenty  to  twenty-five  pounds 
and  reroasted. 

The  fine-sifted  matt  is  brought  to  the  cooling  place, 
where  it  remains  for  six  or  eight  hours.  The  result  of 
this  process  depends  so  much  on  the  roasting  that  at 
Freiberg  an  arrangement  is  made,  according  to  which 


278  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

the  roasters  receive  a  premium,  if  the  tailings  are  found 
poorer  than  the  allowance. 

The  lixivation  is  carried  on  with  hot  water  in  wooden 
tubs  similar  to  those  described  in  Augustin's  process. 
They  are  arranged  in  galleries.  On  the  first  there  are 
eight  wooden  cylindrical  lixiviating  tubs,  provided  with 
a  filtering  apparatus.  The  tubs  are  two  and  a  half  feet 
high  and  the  same  width.  At  the  bottom  there  is  a 
cock  through  which  the  filtrate  is  conveyed  into  clear- 
ing tanks,  thirty  feet  long,  one  and  one-half  feet  wide, 
and  one  and  one-half  feet  deep,  divided  into  two  parti- 
tions. The  lye  enters  the  first  partition,  then  over  the 
parting  board  into  the  second.  From  thence  it  flows 
through  ten  cocks  into  as  many  precipitating  tubs, 
which  are  posted  on  the  second  gallery.  These  tubs 
are  also  provided  with  filters  and  cocks.  Each  of  them 
contains  ten  pounds  of  granulated  copper,  and  over  it 
in  each  two  hundred  and  fifty  pounds  of  black  copper, 
fourteen  inches  long,  five  wide  and  one  inch  thick. 

The  fluid,  after  passing  the  tubs  of  the  second  gallery, 
flows  into  precipitating  tubs  on  the  third  gallery  of 
which  there  are  five  in  number,  containing  likewise 
copper  for  precipitation.  From  this  last  gallery  the 
fluid  flows  into  a  leaden  basin,  wherefrom  it  is  pumped 
into  another  leaden  basin  and  heated  by  steam  till  it 
assumes  a  temperature  of  158°  Fahrenheit. 

The  fine-sifted  matt,  after  having  rested  for  about 
eight  hours  is  cooled  down  to  about  158°  Fahrenheit. 
In  this  state  it  is  introduced  into  the  precipitating  tubs 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  279 

of  the  first  gallery  (four  hundred  pounds  in  each)  and 
water  added  till  it  commences  to  run  out  at  the  cock  on 
the  bottom.  The  water  is  previously  heated  by  steam 
to  158°  Fahrenheit. 

The  water  must  be  stopped  as  soon  as  it  begins  to 
run  through  the  cock,  and  then  so  much  of  the  heated 
fluid  of  the  leaden  basin  is  allowed  to  flow  on  the  matt, 
till  a  sample  from  the  outflow  does  not  show  a  precipi- 
tate of  chloride  of  silver  by  salt  solution.  This  lixivia- 
tion  takes  two  hours  and  a  half.  The  tailings  are 
removed  and  given  over  to  the  copper-smelting  process. 
The  precipitation  of  silver  by  copper  in  the  precipitating 
tubs,  is  similar  to  the  operation  described  in  Augustin's 
process. 

D.    PATERA'S  SILVER  EXTRACTING  PROCESS. 

Sec  78.  By  a  chloridizing  roasting  the  silver  is  con- 
verted into  chloride  of  silver,  then  dissolved  in  hypo- 
sulphite of  soda,  and  precipitated  by  polysulphide  of 
sodium. 

Cold,  diluted  hyposulphite  of  soda  dissolves  the  chlo- 
ride of  silver  sooner  than  a  hot  concentrated  solution  of 
salt.  The  polysulphide  of  sodium  precipitates  the  silver 
as  a  sulphide,  the  reduction  of  which  is  performed  by 
simply  calcining  under  a  muffle. 

The  ore  is  first  subjected  to  an  oxydizing  roasting,  in 
which  the  heat  must  be  increased  slowly  by  degrees, 
especially  if  the  ore  contains  many  different  sulphurets. 


280  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

When  red  heat  is  obtained,  some  steam  is  introduced 
in  the  furnace  and  as  much  as  possible  without  dimin- 
ishing the  necessary  heat.  The  ore  must  be  constantly 
stirred.  In  about  four  hours  the  first  roasting  is  com- 
pleted and  the  ore  is  discharged.  This  must  be  ground 
fine,  mixed  with  from  six  to  ten  per  cent,  of  salt,  or 
more  according  to  the  richness,  and  subjected  to  the 
second — chlorodizing  roasting.  Two  or  three  per  cent, 
of  calcined  green  vitriol  is  added  for  the  decomposition 
of  salt.  When  red-hot,  the  steam  is  used  again,  and 
diligent  stirring  kept  up  for  five  or  six  hours.  Rich 
ore  may  require  a  longer  roasting  by  several  hours. 

The  roasted  ore  is  now  ready  for  lixiviation.  There 
are  chlorides  of  different  base  metals  in  the  ore,  which 
are  soluble  in  water,  while  the  chloride  of  silver  resists, 
for  this  reason  two  lixiviations  are  adopted :  the  first 
with  hot  water,  which  will  dissolve  and  carry  off  the 
chlorides  and  sulphates  of  copper,  iron,  zinc,  cobalt,  etc., 
and  the  second  with  hyposulphite  of  soda  which  dis- 
solves the  chloride  of  silver.  If  the  roasting  is  not  well 
performed  so  that  some  sulphate  of  silver  remains  in 
the  ore,  this  will  be  also  dissolved  by  the  water  and  car- 
ried out  with  the  base  metals. 

Charges  of  four  hundred  pounds  of  roasted  ore  are 
thrown  into  tubs,  prepared  for  lixiviation  like  those  used 
and  described  in  Augustin's  process.  Hot  water  is  con- 
veyed to  the  tubs  for  about  six  hours  by  a  constant 
stream,  purifying  thus  the  mass  of  base  metals.  After 
this  cold  water  is  used  for  the  purpose  of  cooling  the 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  281 

ore,  which  is  not  allowed  to  be  warm  for  the  second 
lixiviation. 

When  cold,  the  ore  must  be  removed  in  other  tubs  of 
the  same  description,  but  smaller.  A  cold  solution  of 
hyposulphite  of  soda  is  brought  into  the  tubs,  and  con- 
tinued till  in  a  taken  sample  no  precipitate  of  silver  is 
obtained  by  a  solution  of  polysulphide  of  sodium. 

The  solution,  now  in  precipitating  tubs,  is  mixed 
together  under  good  stirring  with  the  precipitant  (poly- 
sulphide of  sodium).  The  precipitate  (sulphide  of  silver) 
appears  black.  Attention  is  necessary  to  use  the  right 
proportion  of  the  precipitant,  in  order  to  obtain  a  neu- 
tral liquor  after  all  the  silver  is  precipitated.  This  fluid 
is  used  over  again  for  lixiviation,  but  a  surplus  of  the 
precipitant  would  render  the  fluid  unsuitable  for  that 
purpose  and  precipitate  some  silver  in  the  mass  during 
the  lixivation.  If  no  more  precipitation  is  observed,  a 
small  quantity  of  the  solution  is  taken  in  a  glass  tube 
and  some  drops  of  polysulphide  of  sodium  added.  If  a 
black  precipitate  is  produced  in  a  slight  degree,  some 
more  of  the  precipitant  must  be  added  to  the  solution 
in  the  precipitating  tubs ;  but  if,  on  the  contrary,  no 
precipitate  was  obtained  in  the  glass  tube,  another  sam- 
ple must  be  taken,  and  tried  with  some  drops  of  the 
original  solution.  If  then  a  black  precipitate  is  formed, 
too  much  of  the  precipitant  was  introduced  into  the 
precipitating  tub  and  must  be  neutralized  by  addition 
of  the  original  solution. 

The  precipitated  black  sulphide  of  silver  deposits  in 


282  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


bags  which  are  well  pressed,  dried,  then  washed  with 
warm  water  in  filters,  dried  again  and  heated  under 
muffles,  to  which  air  has  access.  The  sulphur  burns  off 
and  the  silver  remains  in  metallic  condition.  This  is 
melted  finally  in  crucibles  with  an  addition  of  some  iron 
and  borax. 


TABLE  I 


SHOWING  THE  AMOUNT  OF  SILVER  OR  GOLD  IN  OUNCES  CON- 
TAINED IN  ONE  TON  OF  ORE  (TWO  THOUSAND  POUNDS)  FROM 
THE  WEIGHT  OF  FINE  METAL  OBTAINED  IN  AN  ASSAY  OF 
HALF  AN  OUNCE  OR  TWO  HUNDRED  AND  FORTY  GRAINS  OF 
ORE. 


284  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


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•060 

72-90 

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1-21 

1 

37-66 

1 

74-11 

2 

2-43 

2 

38-88 

2 

75-33 

3 

3-64 

3 

40-09 

3 

76-54 

4 

4-86 

4 

41-31 

4 

77-76 

5 

6-07 

5 

42-52 

5 

78-97 

6 

7-29 

6 

43-74 

6 

80-19 

7 

8-50 

7 

44-95 

7 

81-40 

8 

9-72 

8 

46-17 

8 

82-62 

9 

10-93 

9 

47-38 

9 

83-83 

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12-15 

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48-60 

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85-05 

1 

13-36 

1 

49-81 

1 

86-26 

2 

14-58 

2 

51-03 

2 

87-48 

3 

15-79 

3 

52-24 

3 

88-69 

4 

17-01 

4 

53-46 

4 

89-91 

5 

18-22 

5 

54-67 

R 
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91-12 

6 

19-43 

6 

55-89 

6 

92-34 

7 

20-65 

7 

57-10 

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93-55 

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21-86 

8 

58-32 

8 

94-77 

9 

23-08 

9 

59-53 

9 

95-98 

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24-30 

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60-75 

•080 

97-20 

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25-51 

1 

61-96 

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98-41 

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26-73 

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63-18 

2 

99-63 

3 

27-94 

3 

64-39 

3 

100-84 

4 

29-16 

4 

65-61 

4 

102-06 

5 

30-37 

5 

66-82 

5 

103-27 

6 

31-59 

6 

68-04 

6 

104-49 

7 

32-80 

7 

69-25 

7 

105-70 

8 

34-02 

8 

70-47 

8 

106-92 

9 

35-23 

9 

71-68 

9 

108-13 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  285 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


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•120 

145-80 

•150 

182-25 

1 

110-56 

1 

147-01 

1 

183-46 

2 

111-78 

2 

148-23 

2 

184-68 

3 

112-99 

3 

149-44 

3 

185-89 

4 

114-21 

4 

150-66 

4 

187-11 

5 

115-42 

5 

151-87 

5 

188-32 

6 

116-64 

6 

153-09 

6 

189-54 

7 

117-85 

154-30 

7 

190-75 

8 

119-07 

8 

155-52 

8 

191-97 

9 

120-28 

9 

156-73 

9 

193-18 

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121-50 

•130 

157-95 

•160 

194-40 

1 

122-71 

1 

159-16 

1 

195-61 

2 

123-93 

2 

160-38 

2 

196-83 

3 

125-14 

3 

161-59 

3 

198-04 

4 

126-36 

4 

162-81 

4 

199-26 

5 

127-57 

5 

164-02 

5 

200-47 

6 

128-79 

6 

165-24 

6 

201-69 

7 

130-00 

5 

166-45 

7 

202-90 

8 

131-22 

167-67 

8 

204-12 

9 

132-43 

168-88 

9 

205-33 

•110 

133-65 

:  '140 

170-10 

•170 

206-55 

1 

134-86 

1 

171-31 

1 

207-76 

2 

136-08 

2 

172-53 

2 

208-98 

3 

137-29 

3 

173-74 

3 

210-19 

4 

138-51 

4 

174-96 

4 

211-41 

5 

139-72 

5 

176-17 

5 

212-62 

6 

140-94 

6 

177-39 

6 

213-84 

7 

142-15 

7 

178-60 

7 

215-05 

8 

143-37 

8 

179-82 

8 

216-27 

9 

144-58 

1  9 

181-03 

9 

217-48 

286  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  P 


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218-70 

•210 

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•240 

291-60 

1 

219-91 

1 

256-36 

1 

292-81 

2 

221-13 

2 

257-58 

2 

294-03 

3 

222-34 

3 

258-79 

3 

295-24 

4 

223-56 

4 

260-01 

4 

296-46 

5 

224-77 

5 

261-22 

5 

297-67 

6 

225-99 

6 

262-44 

6 

398-89 

7 

227-20 

7 

263-65 

7 

300-10 

8 

228-42 

8 

264-87 

8 

301-32 

9 

229-63 

9 

266-08 

9 

302-53 

•190 

230-85 

•220 

267-30 

•250 

303-75- 

1 

232-06 

1 

268-51 

1 

304-96 

2 

233-28 

2 

269-73 

2 

306-18 

3 

234-49 

3 

270-94 

3 

307-39 

4 

235-71 

4 

272-16 

4 

308-61 

5 

236-92 

5 

273-37 

5 

309-82 

6 

238-14 

6 

274-59 

6 

311-04 

7 

239-35 

7 

275-80 

7 

312-25 

8 

240-57 

8 

277-02 

8 

313-47 

9 

241-78 

9 

278-23 

9 

314-68 

•200 

243-00 

•230 

279-45 

•260 

315-90 

1 

244-21 

1 

280-66 

1 

317-11 

2 

245-43 

2 

281-88 

2 

318-33 

3 

246-64 

3 

283-09 

3 

319-54 

4 

247-86 

4 

284-31 

4 

320-76 

5 

249-07 

5 

285-52 

5 

321-97 

6 

250-29 

6 

286-74 

6 

323-19 

7 

251-50 

7 

287-95 

7 

324-40 

8 

252-72 

8 

289-17 

8 

325-62 

9 

253-93 

9 

290-38 

9 

326-83 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  287 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  Con- 

Fine Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

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•310 

376-65 

•340 

413-10 

1 

341-41 

1 

377-86 

1 

414-31 

2 

342-63 

2 

379-08 

2 

415-53 

3 

343-84 

3 

380-29 

3 

416-74 

4 

345-06 

4 

381-51 

4 

417-96 

5 

346-27 

5 

382-72 

5 

419-17 

6 

347-49 

6 

383-94 

6 

420-39 

7 

348-70 

7 

385-15 

7 

421-60 

8 

349-92 

8 

386-37 

8 

422-82 

9 

351-13 

9 

387-58 

9 

424-03 

•290 

352-35 

•320 

388-80 

•350 

425-25 

1 

353-56 

1 

390-01 

1 

426-46 

2 

354-78 

2 

391-23 

2 

427-68 

3 

355-99 

3 

392-44 

3 

428-89 

4 

357-21 

4 

393-66 

4 

430-11 

5 

358-42 

5 

394-87 

5 

431-32 

6 

359-64 

6 

396-09 

5 

432-54 

7 

360-85 

7 

397-30 

7 

433-75 

8 

362-07 

8 

398-52 

8 

434-97 

9 

363-28 

9 

399-73 

9 

436-18 

288  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

•360 

437-40 

•390 

473-85 

•420 

510-30 

1 

438-61 

1 

475-06 

1 

511-51 

2 

439-83 

2 

476-28 

2 

512-73 

3 

441-04 

3 

477-49 

3 

513-94 

4 

442-26 

4 

478-71 

4 

515-16 

5 

443-47 

5 

479-92 

5 

516-37 

6 

444-69 

6 

481-14 

6 

517-59 

7 

445-90 

7 

482-35 

7 

518-80 

8 

447-12 

8 

483-57 

8 

520-02 

9 

448-33 

9 

484-78 

9 

521-23 

•370 

449-55 

•400 

486-00 

•430 

522-45 

1 

450-76 

1 

487-21 

1 

523-66 

2 

451-98 

2 

488-43 

2 

524-88 

3 

453-19 

3 

489-64 

3 

526-09 

4 

454-41 

4 

490-86 

4 

527-31 

5 

455-62 

5 

492-07 

5 

528-52 

6 

456-84 

6 

493-29 

6 

529-74 

7 

458-05 

7 

494-50 

7 

530-95 

8 

459-27 

8 

495-72 

8 

532-17 

9 

460-48 

9 

496-93 

9 

533-38 

•380 

461-70 

•410 

498-15 

•440 

534-60 

1 

462-91 

1 

499-36 

1 

535-81 

2 

464-13 

2 

500-58 

2 

537-03 

3 

465-34 

3 

501-79 

3 

538-24 

4 

466-56 

4 

503-01 

4 

539-46 

5 

467-77 

5 

504-22 

5 

540-67 

6 

468-99 

6 

505-44 

6 

541-89 

7 

470-20 

7 

506-65 

7 

543-10 

8 

471-42 

8 

507-87 

8 

544-32 

9 

472-63 

9  1 

509-08 

9 

545-53 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  289 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

•450 

C  A  f*  TC 

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A  OA 

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coo  OA 

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£J  OA.  Qd 

bzlrob 

O 

A 

C  A  A  "1  O 

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o 

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C  A  1  1  O 

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£?0  A.  C  O 

•460 

558-90 

•490 

595-35 

•520 

631-80 

1 

560-11 

1 

596-56 

1 

633-01 

2 

561-33 

2 

597-78 

2 

634-23 

3 

562-54 

3 

598-99 

3 

635-44 

4 

563-76 

4 

600-21 

4 

5 

564-97 

5 

601-42 

5 

637-87 

6 

566-19 

6 

602-64 

6 

639-09 

7 

567-40 

7 

603-85 

7 

640-30 

8 

568-62 

8 

605-07 

8 

641-52 

9 

569-83 

9 

606-28 

9 

642-73 

•470 

571-05 

•500 

607-50 

•530 

643-95 

1 

572-26 

1 

608-71 

1 

645-16 

2 

573-48 

2 

609-93 

2 

646-38 

3 

574-69 

3 

611-14 

3 

647-59 

4 

575-91 

4 

612-36 

4 

648-81 

5 

577-12 

5 

613-57 

5 

650-02 

6 

578-34 

6 

614-79 

6 

651-24 

7 

579-55 

7 

616-00 

7 

652-45 

8 

580-77 

8 

617-22 

8 

653-67 

9 

581-98 

9 

618-43 

9 

654-88 

19 


290  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds, 


*4 
o  5" 

o 
<-+  » 

fed 

a  I' 

o 

c 

P  © 

i  Metal  — 
'  the  unit  c 

ton  of  0] 
in  —  Oun( 

i  Metal  — 
'  the  unit  c 

ton  of  0] 
in  —  Oun< 

3  Metal  — 
'  the  unit  c 

ton  of  oi 
in  —  Oun< 

Thoust 
»f  10  grc 

re  will 

Thousj 
>f  10  grf 

re  will 

°  5 
cr?  d 
2  SS 

re  will  i 

tnds 
tins. 

o 
o 

:  p 

mds 
tins. 

o 
o 
IjJ 

mds 
tins. 

o 
O 

•  ° 

•540 

65640 

C  IT  A 

•5<0 

692-55 

r>  r\  r\ 

•600 

729-00 

1 

657-31 

1 

693-76 

1 

730-21 

2 

658-53 

2 

694-98 

2 

731-43 

3 

659-74 

3 

696-19 

3 

732-64 

4 

660-96 

A 

4 

697-41 

A 

4 

733-86 

5 

662-17 

5 

698-62 

5 

735-07 

6 

663-39 

6 

699-84 

6 

736-29 

7 

664-60 

7 

701-05 

rr 

7 

737-50 

o 

8 

665-82 

8 

702-27 

o 

8 

738-72 

9 

667-03 

9 

703-48 

9 

739-93 

•550 

668-25 

•580 

704-70 

•610 

741-15 

1 

669-46 

1 

705-91 

1 

742-36 

2 

D  I  U'OO 

2 

707.1  3 

2 

3 

671-89 

3 

708-34 

3 

744-79 

4 

673-11 

4 

709-56 

4 

746-01 

5 

674-32 

5 

710-77 

5 

747-22 

6 

675-54 

6 

711-99 

6 

748-44 

7 

676-75 

7 

713-20 

7 

749-65 

8 

677-97 

8 

714-42 

8 

650-87 

9 

679-18 

9 

715-63 

9 

752-08 

•560 

680-40 

•590 

716-85 

•620 

753-30 

1 

681-61 

1 

718-06 

1 

754-52 

2 

682-83 

2 

719-28 

2 

755-74 

3 

684-04 

3 

720-49 

3 

756-95 

4 

685-26 

4 

721-71 

4 

758-17 

5 

686-47 

5 

722-92 

5 

759-38 

6 

687-69 

6 

724-14 

6 

760-59 

7 

688-90 

7 

725-35 

7 

761-80 

8 

690-12 

8 

726-57 

8 

763-02 

9 

691-33 

9 

727-78 

9 

764-23 

PKOCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  291 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 
tain —  Ounces  

•boO 

7£?  C  /<  c 

•bbU 

O  A1  AA 

a  aa 

QO  O  Of 
OOO'OO 

1 

i  bb  bb 

1 
1 

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A 

1  b  i  -oo 

0 

A 

Q  A  A  .  O  O 

0 
A 

Q  A  A .  7  Q 

o 

6 

7£JO  AO 

0 

6 

oUo-o4 

0 
0 

Q/M  AA 

o4±-yy 

A 

4 

77A.01 

A 

4 

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A 

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r 
0 

771 .£0 

r 
0 

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b 

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779.  OC 

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Q 
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y 

77/3  O O 

y 

OI  O  QO 

y 

•640 

777-60 

•670 

814-05 

•700 

850-50 

1 

778-82 

1 

815-26 

1 

851-71 

2 

780-04 

2 

816-48 

2 

852-93 

3 

781-25 

3 

817-69 

3 

854-14 

4 

782-47 

4 

818-91 

4 

855-36 

5 

783-68 

5 

820-12 

5 

856-57 

6 

784-90 

6 

821-34 

6 

857-79 

7 

786-11 

7 

822-55 

7 

859-00 

8 

787-33 

8 

823-77 

8 

860-22 

9 

788-54 

9 

824-98 

9 

861-43 

•650 

789-75 

•680 

826-20 

•710 

862-65 

1 

790-96 

1 

827-41 

1 

863-86 

2 

792-18 

2 

828-63 

2 

865-08 

3 

793-39 

3 

829-84 

3 

866-29 

4 

794-61 

4 

831-06 

4 

867-51 

5 

795-82 

5 

832-27 

5 

868-72 

6 

797-04 

6 

833-49 

6 

869-94 

7 

798-25 

7 

834-70 

7 

871-15 

8 

799-47 

8 

835-92 

8 

872-37 

9 

800-68 

9 

837-13 

9 

873-58 

292  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

•720 

874-80 

•750 

911-2o 

•780 

947-70 

1 

876-01 

1 

912-46 

1 

948-91 

2 

8<  7-23 

2 

913-68 

2 

950-13 

3 

878-44 

3 

914-89 

3 

951-34 

4 

879-66 

4 

916-11 

4 

952-56 

5 

a  a  a  nrr 

880-87 

5 

917-32 

5 

953-77 

6 

AAA  AA 

882-09 

6 

918-o4 

6 

954-99 

7 

AAA     A  /\ 

883-30 

7 

919-75 

7 

956-20 

8 

884-52 

8 

AAA    A  rr 

920-9^ 

8 

957-42 

9 

885-73 

9 

922-18 

9 

958-63 

•730 

886-95 

•760 

923-40 

•790 

959-85 

1 

888-16 

1 

924-61 

1 

961-06 

2 

889-38 

2 

925-83 

2 

962-28 

3 

890-59 

3 

927-04 

3 

963-49 

4 

891-81 

4 

928-26 

4 

964-71 

5 

893-02 

5 

929-47 

5 

965-92 

6 

894-24 

6 

930-69 

6 

967-14 

7 

895-45 

7 

931-90 

7 

968-35 

8 

896-67 

8 

933-12 

8 

969-57 

9 

897-88 

9 

934-33 

9 

970-78 

•740 

899-10 

1  -770 

935-55 

•800 

972-00 

1 

900-31 

936-76 

1 

973-21 

2 

901-53 

937-98 

2 

974-43 

3 

902-74 

3 

939-19 

3 

975-64 

4 

903-96 

4 

940-41 

4 

976-86 

5 

905-17 

5 

941-62 

5 

978-07 

6 

906-39 

6 

942-83 

6 

979-29 

7 

907-60 

7 

944-05 

7 

980-50 

8 

908-82 

8 

945-27 

8 

981-72 

9 

910-03 

9 

946-48 

9 

982-93 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  293 


Chinees  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

One  ton  of  ore  will  con- 

Fine  Metal  —  Thousands 
of  the  unit  of  10  grains. 

i 

One  ton  of  ore  will  con- 

Oi  A 

•oil) 

Q  Q  \  .  1  £ 

.  Q  i  n 

1  non.en 

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1 

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1 

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A 

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Q 

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1  AO  |.0( 

Q 
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A 

4 

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A 

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1  A£1 .01 

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0 

GQA.OO 

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r 
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1  AeQ.1  O 

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996-30 

•850 

1032-75 

•880 

1069-20 

1 

997-51 

1 

1033-96 

1 

1070-41 

2 

998-73 

2 

1035-18 

2 

1071-63 

3 

999-94 

3 

1036-39 

3 

1072-84 

4 

1001-16 

4 

1037-61 

4 

1074-06 

5 

1002-37 

5 

1038-82 

5 

1075-27 

6 

1003-59 

6 

1040-04 

6 

1076-49 

7 

1004-80 

7 

1041-25 

7 

1077-70 

8 

1006-02 

8 

1042-47 

8 

1078-92 

9 

1007-23 

9 

1043-68 

9 

1080-13 

•830 

1008-45 

•860 

1044-90 

•890 

1081-35 

1 

1009-66 

1 

1046-11 

1 

1082-56 

2 

1010-88 

2 

1047-33 

2 

1083-78 

3 

1012-09 

3 

1048-54 

3 

1084-99 

4 

1013-31 

4 

1049-76 

4 

1086-21 

5 

1014-52 

5 

1050-97 

5 

1087-42 

6 

1015-74 

6 

1052-19 

6 

1088-64 

7 

1016-95 

7 

1053-40 

7 

1089-85 

8 

1018-17 

8 

1054-62 

8 

1091-07 

9 

1019-38 

9 

1055-83 

9 

1092-28 

294  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds. 


o 

H 

c 

o 

&  3" 

i  § 

2.  a* 

r+  B 

S°  (5 

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1  § 

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1  § 

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unit 

p  ~> 

0  2- 
p  SL 

§  2> 

tal- 
unit 

p 

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P  o 
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ains. 

o 

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ands 
ains. 

8 

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ands 
ains. 

o 

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AAA 

1093-50 

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1129-95 

•you 

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1166-40 

i 

1094-71 

1 

1131-16 

1 

1167-61 

o 

1095-93 

1132-38 

o 

1168-83 

O 

o 

1097-14 

o 
o 

1133-59 

o 
o 

1170-04 

4 

1098-36 

4 

1134-81 

4 

1171-26 

0 

1099-57 

er 
O 

1136-02 

c 
O 

1172-47 

n 
0 

1100-79 

£» 
0 

1137-24 

O 

1173-69 

rr 
< 

1102-00 

rr 
i 

1138-45 

7 

1174-90 

Q 

O 

1103-22 

Q 
O 

1139-67 

Q 
O 

1176-12 

y 

1104-43 

y 

1140-88 

y 

1177-33 

•910 

1105-65 

•940 

1142-10 

•970 

1178-55 

l 

1106-86 

1 

1143-31 

1 

1179-76 

2 

1108-08 

2 

1144-53 

2 

1180-98 

3 

1109-29 

3 

1145-75 

3 

1182-19 

4 

1110-51 

4 

1146-96 

4 

1183-41 

5 

1111-72 

5 

1148-17 

5 

1184-62 

6 

1112-94 

6 

1149-39 

6 

1185-84 

7 

1114-15 

7 

1150-60 

7 

1187-05 

8 

1115-37 

8 

1151-82 

8 

-1188-27 

9 

1116-58 

9 

1153-03 

9 

1189-48 

•920 

111  roU 

•950 

llo4*ZO 

•980 

i  "1  OA  TA 

iiyu-70 

1 

1119-01 

1 

1155-46 

1 

1191-91 

2 

1120-23 

2 

1156-68 

2 

1193-13 

3 

1121-44 

3 

1157-89 

3 

1194-34 

4 

1122-66 

4 

1159-11 

4 

1195-56 

5 

1123-87 

5 

1160-32 

5 

1196-77 

6 

1125-09 

6 

1161-54 

6 

1197-99 

7 

1126-30 

7 

1162-75 

7 

1199-20 

8 

1127-52 

8 

1163-97 

8 

1200-42 

9 

1128-73 

9 

1165-18 

9 

1201-63 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  295 


Ounces  of  Fine  Metal  per  Ton  of  Ore  of  2,000  Pounds, 


fed 

o  5' 

>t>  CD 

o  P* 

r+  P 

£2.  © 

o  p' 

-*>  CD 

r+  P 
£0  CD 

f  g 

P 

1  ° 
1  » 

e-h 

P°  <-h 
1  ° 

P*  fe" 
CD  h-l 

1  » 

etal- 
i  unit 

p  ~» 

P  o 

etal- 
unit 

P  ^ 

etal- 
unit 

P 

o  1 

O 

CD  CD 
CO 

o  I 

P  o 

O 

CD  CD 
CO 

O  1 

P  o 

CD  CD 
CO 

s  r 

:  * 

®  g* 

:  3 

<=>  §* 

:  3 

cr?  p 

"I  CO 

QK5  P 

i-S  SO 

CK?  p 

>-«  CO 

ands 
ains. 

o 
o 

•  ? 

ands 
ains. 

C5 

o 

:  p 

ands 
ains. 

o 
o 

•  p 

•990 

1202-85 

•995 

1208-92 

1-000 

1215-00 

1 

1204-06 

6 

1210-14 

2-000 

2430-00 

2 

1205-28 

7 

1211-35 

3-000 

3645-00 

3 

1206-49 

8 

1212-57 

4-000 

4860-00 

4 

1207-71 

9 

1213-78 

5-000 

6075-00 

TABLE  II 


SHOWING  THE  VALUE  OF  SILVER  PER  OUNCE  TROY  AS  AL- 
LOYED IN  THE  BAR  WHEN  THE  STANDARD  IS  EXPRESSED 
IN  THOUSANDTHS. 

20 


298  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


Value  of  /Silver  per  Ounce  Troy  at  different  Fineness. 


H 

u 

H 

0 

O 

CD 

a 

CD 

p* 
o 
P 

g 

o 
p- 

CO 

§ 

CO 

tr 
o 
a 

CO 

P 

p- 

5!  • 

P 

CO 

p- 

CO 

p 

p" 

CO 

P 
<-t- 

co 

p 

<->. 

; 

If 

• 

p* 

: 
j 

5' 

p 

; 
? 

i 

00-06 

•030 

03-88 

•060 

07-76 

•001 

00-13 

1 

04-01 

1 

07-89 

2 

00-26 

2 

04-14 

2 

08-02 

3 

00-39 

3 

04-27 

3 

08-15 

4 

09-52 

4 

04-40 

4 

08-28 

5 

00-65 

5 

04-53 

5 

08-41 

6 

00-78 

6 

04-66 

6 

08-53 

7 

00-91 

7 

04-78 

7 

08-66 

8 

01-04 

8 

04-91 

8 

08-79 

9 

01-17 

9 

05-04 

9 

08-92 

•010 

01-29 

•040 

05-17 

•070 

09-05 

1 

01-42 

1 

05-30 

1 

09-18 

2 

01-55 

2 

05-43 

2 

09-31 

3 

01-68 

3 

05-56 

3 

09-44 

4 

01-81 

4 

05-69 

4 

09-57 

5 

01-94 

5 

05-82 

5 

09-70 

6 

02-07 

6 

05-95 

6 

09-83 

7 

02-20 

7 

06-08 

7 

09-96 

8 

02-33 

8' 

06-21 

8 

10-09 

9 

02-46 

9 

06-34 

9 

10-21 

Ar»  a 

•020 

02-58 

A  f  A 

•050 

06-46 

AO  A 

•080 

-i  A  O  A 

10-34 

1 

02-71 

1 

06-59 

1 

10-47 

2 

02-83 

2 

06-72 

2 

10-60 

3 

02-96 

3 

06-85 

3 

10-73 

4 

03-09 

4 

06-98 

4 

10-86 

5 

03-22 

5 

07-11 

5 

10-99 

6 

03-35 

6 

07-24 

6 

11-12 

7 

03-49 

7 

07-37 

7 

11-25 

8 

03-62 

8 

07-50 

8 

11-38 

9 

03-75 

9 

07-63 

9 

11-51 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  299 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


H 

u 

o 

o 

o 

CD 

U 

O 

&• 
p 

o 

1 

p 

co 

P 

o 
p* 

P 

DO 

tr 
p 

p* 

p 

CO 

CO 

p 

CO 

CO 

p 

CO 

CO 

p 

Pi 

a 
P* 

: 

§ 

& 

co 

* 

& 

CO 

CO 

5" 

p 

• 

B' 

P 

j 

•090 

11-64 

•120 

15-52 

•150 

19-39 

1 

11-77 

1 

15-64 

1 

19-52 

2 

11-89 

2 

15-77 

2 

19-65 

3 

12-02 

3 

15-90 

3 

19-78 

4 

12-15 

4 

16-03 

4 

19-91 

5 

12-28 

5 

16-16 

5 

20-04 

6 

12-41 

6 

16-29 

6 

20-17 

7 

12-54 

7 

16-42 

7 

20-30 

8 

12-67 

8 

16-55 

8 

20-43 

9 

12-80 

9 

.16-68 

9 

20-56 

•100 

12-93 

•130 

16-81 

•160 

20-69 

1 

13-06 

1 

16-94 

1 

20-82 

2 

13-19 

2 

17-07 

2 

20-95 

3 

13-32 

3 

17-20 

3 

21-08 

4 

13-45, 

4 

17-33 

4 

21-21 

5 

13-58 

5 

17-45 

5 

21-33 

6 

13-71 

6 

17-58 

6 

21-46 

7 

13-83 

7 

17-71 

7 

21-59 

8 

13-96 

8 

17-84 

8 

21-72 

9 

14-09 

9 

17-97 

9 

21-85 

•110 

-t  a  curt 

14-22 

•140 

^  Q   -J  A 

lev 

-t  <T  A 

•170 

Cfi  AO 

21-98 

1 

14-35 

1 

18-23 

1 

22-11 

2 

14-48 

2 

18-36 

2 

22-24 

3 

14-61 

3 

18-49 

3 

22-37 

4 

14-74 

4 

18-62 

4 

22-50 

5 

14-87 

5 

18-75 

5 

22-63 

6 

15-00 

6 

18-88 

6 

22-75 

7 

15-13 

7 

19-01 

7 

22-88 

8 

15-26 

8 

19-14 

8 

23-01 

9 

15-39 

9 

19-26 

9 

23-14 

300  PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION. 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


L2 

w 

3 

T>  ' 

i_J 
HS 

3 

•n 

0 

C  J 

o 

o 

0 

& 
O 

i 

0^ 

3 

rt- 
O 

0 

S3 

0 

CD 
0 
CO 

CO 

to 
S3 

5 

2 

CO 

CO 

>-« 

CO 

S3- 

CO 

Cu 

CO 

1 

CO 

a 
p 

CD 

O 

: 
* 

480 

90.97 

Z  O  Z  1 

•210 

97-1  ^ 

Z I  L'J 

•240 

31-03 

1 

ZO  rrv 

1 

97*98 

Z  t  zo 

1 

31-16 

2 

ZO  OO 

2 

97-41 

2 

31-29 

3 

ZO  uu 

3 

97-^4 
z  1 

3 

31-42 

4 

ZO   1  >_' 

4 

97-fi7 
z  t  u  1 

4 

31-55 

5 

90.09 

5 

97*80 

Z  1  CJ 

5 

31-68 

6 

94-0^ 
z*±  yjo 

6 

z  1  00 

6 

31-81 

7 

Zt  IO 

7 

ZO  vU 

7 

31-94 

8 

Z^±  OJL 

8 

98-1  Q 

ZO  ±t7 

8 

32-06 

9 

94.  «44. 

Z^±  tct: 

9 

9Q.O9 

ZO  oz 

9 

32-19 

•190 

24-57 

•220 

28-44 

•250 

32-32 

1 

24-69 

1 

28-57 

1 

32-45 

2 

24-82 

2 

28-70 

2 

32-58 

3 

24-95 

3 

28-83 

3 

32-71 

4 

25-08 

4 

28-96 

4 

32-84 

5 

25-21 

5 

29-09 

5 

32-97 

6 

25-34 

6 

29-22 

6 

33-10 

7 

25-47 

7 

29-35 

7 

33-23 

8 

25-60 

8 

29-48 

8 

33-36 

9 

25-73 

9 

29-61 

9 

33-49 

•200 

25-86 

•230 

29-74 

•260 

33-62 

1 

25-99 

1 

29-87 

1 

33-75 

2 

26-12 

2 

30-00 

2 

33-87 

3 

26-25 

3 

30-13 

3 

34-00 

4 

26-38 

4 

30-26 

4 

34-13 

5 

26-50 

5 

30-38 

5 

34-26 

6 

26-63 

6 

30-51 

6 

34-39 

7 

26-76 

7 

30-64 

7 

34-52 

8 

26-89 

8 

30-77 

8 

34-65 

9 

27-02 

9 

30-90 

9 

34-78 

PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  301 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


b 

« 

a 

H 

0 

( 

~i 

lousam 

a 
I 

x 

b 

CO 

•> 

6 
-. 

-t- 

o 

o 

(3 

CO 

P 
P 

o 

R 

CO 

CO 

& 

CO 

pj 

CO 

p 

o 

p' 

CD 

? 

•270 

o  /( .n-i 

o4*yl 

•300 

do*  ( y 

•330 

42-57 

1 

do*U4 

1 

oo.no 

1 

a  o  on 

2 

2 

on.  AC 

2 

/<  o  no 

4^-yd 

3 

Q  (".OA 

3 

0O.1  Q 

dy-io 

3 

4  O  At 

4 

O  0 

do*4o 

4 

on  on 

4 

A  O  A  Q 

5 

OO'OO 

5 

on  a  o 
dy-4d 

5 

AO  OA 

4d*dl 

6 

do-by 

6 

on 

dy-Ob 

6 

AO.  A  A 

4d*44 

7 

7 

on  pn 

dy*by 

7 

AO   C  T 

43-57 

8 

o  cn/i 
00*94 

8 

on  oo 

8 

A  O  i"7A 

43-70 

9 

db'Ui 

9 

on  nc 

dy*yo 

9 

o  oo 

•280 

36-20 

•310 

40-08 

•340 

43-96 

1 

36-33 

1 

40-21 

1 

44-09 

2 

36-46 

2 

40-34 

2 

44-22 

3 

36-59 

3 

40-47 

3 

44-35 

4 

36-72 

4 

40-60 

4 

44-48 

5 

36-85 

5 

40-73 

5 

44-61 

D 

36-98 

6 

40-86 

6 

44-74 

7 

37-11 

7 

40-98 

7 

44-86 

8 

37-24 

8 

41-11 

8 

44-99 

9 

37-37 

9 

41-24 

9 

45-12 

•290 

37-50 

•320 

41-37 

OCA 

•350 

45-25 

1 

37-63 

1 

41-50 

1 

45-38 

2 

37-76 

2 

41-63 

2 

45-51 

3 

37-88 

3 

41-76 

3 

45-64 

4 

38-01 

4 

41-89 

4 

45-77 

5 

38-14 

5 

42-02 

5 

45-90 

6 

38-27 

6 

42-15 

6 

46-03 

7 

38-40 

7 

42-28 

7 

46-16 

8 

38-53 

8 

42-41 

8 

46-29 

9 

38-66 

9 

42-54 

9 

46-42 

302  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


b 

9 

H 

b 

o 

Q 

$ 

b 

o 

<6 

lousanc 

5 

DO 
j 

lousanc 

p 

B 

CO 

p 

CO 

§ 

a" 
e 

J3 

CO 

CO 

• 

• 

»— ' 

CO 

• 

CO 

* 

j 

: 
• 

p 

o 

; 

p" 
o 

; 
1 

•360 



46-55 

•390 

50-42 

•420 

54-30 

1 

46-67 

1 

50-55 

1 

54-43 

2 

46-80 

2 

50-68 

2 

54-56 

3 

46-93 

3 

50-81 

3 

54-69 

4 

47-06 

4 

50-94 

4 

54-82 

5 

47-19 

5 

51-07 

5 

54-95 

6 

47-32 

6 

51-20 

6 

55-08 

7 

47-45 

7 

51-33 

7 

55-21 

8 

47-58 

8 

51-40 

8 

55-34 

9 

47-71 

9 

51-59 

9 

55-47 

•370 

47-84 

•400 

51-72 

•430 

55-60 

1 

47-97 

1 

51-85 

1 

55-73 

2 

48-10 

2 

51-98 

2 

55-85 

3 

48-23 

3 

52-11 

3 

55-98 

4 

48-36 

4 

52-23 

4 

56-11 

5 

48-48 

5 

52-36 

5 

56-24 

u 

48-61 

u 

52-49 

6 

56-37 

7 

48-74 

7 

52-62 

7 

56-50 

8 

48-87 

8 

52-75 

8 

56-63 

9 

49-00 

9 

52-88 

9 

56-76 

•380 

•410 

Oo'Ul 

1     .A  A  f\ 

1 

49-26 

1 

53-14 

1 

57-02 

2 

49-39 

2 

53-27 

2 

57-15 

3 

49-52 

3 

53-40 

3 

57-28 

4 

49-65 

4 

53-53 

4 

57-41 

5 

49-78 

5 

53-66 

5 

57-54 

6 

49-91 

6 

53-79 

6 

57-66 

7 

50-04 

7 

53-92 

7 

57-79 

8 

50-17 

8 

54-04 

8 

57-92 

9 

50-29 

9 

54-17 

9 

58-05 

PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  303 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


G 

O 

o 

G 

o 

CD 

HJ 

G 

O 

CD 

o 

0 

GO 

g 

p* 
3 

p 

CO 

§ 

co 

P 

ST 

CO 

CO 

sr 
o 
c 

CO 

P 

o 
p1 

<r»- 
GO 

* 

p 

D 

pu 

GO 

S1 

CO 

'. 

pi 

GO 

f 

: 

5* 

* 

5* 

• 

-  1  I'' 
• 

j 

•450 

58-18 

•480 

62-06 

•510 

65-94 

1 

58-31 

1 

62-19 

1 

66-07 

2 

58-44 

2 

62-32 

2 

66-20 

3 

58-57 

3 

62-45 

3 

66-33 

4 

58-70 

4 

62-58 

4 

66-46 

5 

58-83 

5 

62-71 

5 

66-59 

6 

58-96 

6 

62-84 

6 

66-72 

7 

59-09 

7 

62-97 

7 

66-84 

8 

59-22 

8 

63-09 

8 

66-97 

9 

59-35 

9 

63-22 

9 

67-10 

•460 

59-47 

•490 

63-35 

•520 

67-23 

1 

59-60 

1 

63-48 

1 

67-36 

2 

59-73 

2 

63-61 

2 

67-49 

3 

59-86 

3 

63-74 

3 

67-62 

4 

59-99 

4 

63-87 

4 

67-75 

5 

60-12 

5 

64-00 

5 

67-88 

6 

60-25 

6 

64-13 

6 

08-01 

7 

60-38 

7 

64-26 

7 

68-14 

8 

60-51 

8 

64-39 

8 

68-27 

9 

60-64 

9 

64-52 

9 

68-40 

•470 

60-77 

•500 

64-65 

•530 

/in  f  o 

68-53 

1 

60-90 

1 

64-78 

1 

68-65 

2 

61-02 

2 

64-91 

2 

68-78 

3 

61-15 

3 

65-03 

3 

68-91 

4 

61-28 

4 

65-16 

4 

69-04 

5 

61-41 

5 

65-29 

5 

69-17 

6 

61-54 

6 

65-42 

6 

69-30 

7 

61-67 

7 

65-65  ' 

7 

69-43 

8 

61-80 

8 

65-68 

8 

69-56 

9 

61-93 

9 

65-81 

9 

69-69 

304  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


1  Dollars  

s 

3 

7: 

•540 

69-82 

•570 

73-69 

•600 

it  rr  f~  n 

77-58 

1 

69-95 

1 

73-82 

1 

77-71 

2 

70-08 

2 

73-95 

2 

77-83 

3 

70-21 

3 

74-08 

3 

77-96 

4 

70-34 

4 

74-21 

4 

78-09 

5 

70-46 

5 

74-34 

5 

78-22 

6 

70-59 

6 

74-47 

6 

•  78-35 

7 

70-72 

7 

74-60 

7 

78-48 

8 

70-85 

8 

74-73 

8 

78-61 

9 

70-98 

9 

74-86 

9 

rr  d  rr  a 

78-74 

•550 

71-11 

•580 

74-99 

•610 

78-87 

1 

71-24 

1 

75-12 

1 

79-00 

2 

71-37 

2 

75-25 

2 

79-13 

3 

71-50 

3 

75-38 

3 

79-26 

4 

71-63 

4 

75-51 

4 

79-39 

5 

71-76 

5 

75-64 

5 

79-52 

6. 

71-89 

6 

75-77 

6 

79-64 

7 

72-02 

7 

75-90 

7 

79-77 

8 

72-15 

8 

76-02 

8 

79-90 

9 

72-27 

9 

76-15 

9 

80-03 

•560 

72-40 

•590 

76-28 

•620 

80-16 

1 

72-53 

1 

76-41 

1 

80-29 

2 

72-66 

2 

76-54 

2 

80-42 

3 

72-79 

3 

76-67 

3 

80-55 

4 

72-92 

4 

76-80 

4 

80-68 

5 

73-05 

5 

76-93 

5 

80-81 

6 

73-18 

6 

77-06 

6 

80-94 

7 

73-31 

7 

77-19 

7 

81-07 

8 

73-44 

8 

77-32 

8 

81-20 

9 

73-56 

9 

77-45 

9 

81-32 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  305 

Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


b 

Q 

1  H 

b 

Q 

b 

O 

O 

o 

o 
p 

o 

o 

CO 

ta 

o 

P 

s 
—. 

fl 

to 

P 
P 

a 

£1 

CO 

1 

g 

so 

6 

pj 

w 

oo 

hrj 

s 

CD 

: 
• 



: 
: 

•630 

81-45 

•660 

85-33 



•690 

89-21 

1 

81-58 

1 

85-46 

1 

89-34 

2 

81-71 

2 

85-59 

2 

89-47 

3 

81-84 

3 

85-72 

3 

89-60 

4 

81-97 

4 

85-85 

4 

89-73 

5 

82-10 

5 

85-98 

5 

89-86 

6 

82-23 

6 

86-11 

6 

8< 

)-99 

7 

82-36 

7 

86-24 

7 

90-12 

8 

82-49 

8 

86-37 

8 

90-25 

9 

82-62 

9 

86-50 

9 

90-38 

•640 

82-75 

i  -670 

86-63 

•700 

90-51 

1 

82-88 

1 

86-76 

1 

90-63 

2 

83-01 

2 

86-88 

2 

90-76 

3 

83-14 

3 

87-01  - 

3 

90-89 

4 

83-27 

4 

87-14 

4 

91-02 

5 

83-39 

5 

87-27 

5 

91-15 

6 

83-52 

6 

87*40 

6 

91-28 

7 

83-65 

I 

87-53 

7 

91-41 

8 

83-78 

87-66 

8 

91-54 

9 

83-91 

9 

87-79 

9 

91-67 

•650 

84-04 

•680 

87-92 

•710 

1  Jl\J 

91-80 

1 

84-17 

1 

88-05 

1 

91-93 

2 

84-30 

2 

88-18 

2 

92-06 

3 

84-43 

3 

88-31 

3 

92-19 

4 

84-56 

4 

88-44 

4 

92-32 

5 

84-69 

5 

88-57 

5 

92-45 

6 

84-82 

6 

88-69 

6 

92-57 

7 

84-94 

7 

88-82 

7 

92-70 

8 

85-07 

8 

88-95 

8 

92-83 

9 

85-20 

9 

89-08 

9 

92-96 

21 


306 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


Dollars  

a 

J 

O 

T 

A 

•720 

93-09 

•750 

96-97 

•780 

1 

00-85 

1 

93-22 

1 

97-10 

1 

1 

00-98 

2 

93-35 

2 

97-23 

2 

1 

01-11 

3 

93-48 

3 

97-36 

3 

1 

01-24 

4 

93-61 

4 

97-49 

4 

1 

01-37 

5 

93-74 

5 

97-62 

5 

1 

01-49 

6 

93-87 

6 

97-75 

6 

1 

0l-62 

7 

94-00 

7 

97-87 

7 

1 

01-75 

8 

94-13 

8 

98-00 

8 

1 

01-88 

9 

94-25 

9 

98-13 

9 

1 

02-01 

t/Tt  oo 

<J  (J  Zj  U 

•7Q0 

i 

JL 

02-14 

1 

94-51 

1 

98-39 

1 

1 

02-27 

2 

94-64 

2 

98-52 

2 

1 

02-40 

3 

94-77 

3 

98-65 

3 

1 

02-53 

4 

94-90 

4 

98-78 

4 

1 

02-66 

5 

95-03 

5 

98-91 

5 

1 

02-79 

6 

95-16 

6 

99-04 

6 

1 

02-92 

7 

95-29 

7 

99-17 

7 

1 

03-05 

8 

95-42 

8 

99-30 

8 

1 

03-18 

9 

95-55 

9 

99-43 

9 

1 

03-31 

•740 

95-68 

•770 

99-56 

•800 

1 

03-43 

1 

95-81 

1 

99-68 

1 

1 

03-56 

2 

95-94 

2 

99-81 

2 

1 

03-69- 

3 

96-06 

3 

99-94 

3 

1 

03-82 

4 

96-19 

4 

1 

00-07 

4 

1 

03-95 

5 

96-32 

5 

1 

00-20 

5 

1 

04-07 

6 

96-45 

6 

1 

00-33 

6 

1 

04-21 

7 

96-58 

7 

1 

00-46 

7 

1 

04-34 

8 

96-71 

8 

1 

00-59 

8 

1 

04-47 

9 

96-84 

9 

1 

00-72 

9 

1 

04-60 

09 

1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 


JESSES  OF  SILVER  AND  GOLD  EXTRACTION.  307 

Silver  per  Ounce  Troy  at  different  Fineness. 


n 

9 

a 

n 

d 

■» 

a 

IT 
-i 

/i 

7) 

9 
0 

U-±  i  o 

0*±U 

-i 

JL 

08-61 

o  (  U 

12-48 

Udb  00 

1 
1 

JL 

08-74 

JL 

± 

12-61 

yj-t  vv 

O 

L 

± 

08 

•86 

o 

A 

i 
i 

12-74 

UO  1.L 

Q 
O 

± 

08-99 

Q 
O 

jl 

12-87 

UO 

I 

0942 

A 

± 

13-00 

UO  o  I 

O 

-I 
1 

09-25 

£ 
0 

-i 
i 

13-13 

UO  ou 

0 

1 

09-38 

0 

i 

13-26 

UO  UO 

1 

1 

Uc/'Ol 

n 
i 

i 
i 

13-39 

UO  1  0 

o 
o 

1 
1 

09-64 

Q 
O 

i 

13-52 

1 

09-77 

g 

-i 
l 

13-65 

08-02 

•850 

1 

09-90 

•880 

1 

13-78 

06-15 

1 

1 

10-03 

1 

1 

13-91 

06-28 

2 

1 

10-16 

2 

1 

14-04 

06-41 

3 

1 

10-29 

3 

1 

14-17 

06-54 

4 

1 

10-42 

4 

1 

14-29 

06-67 

5 

1 

10-55 

5 

1 

14-42 

06-80 

6 

1 

10-67 

6 

1 

14 

•55 

06-93 

7 

1 

10-80 

7 

1 

14-68 

07-05 

8 

1 

10-93 

8 

1 

14-81 

07-18 

9 

1 

11-06 

9 

1 

14-94 

07-31 

•860 

1 

11-19 

•890 

1 

15-07 

07-44 

1 

1 

11-32 

1 

1 

15-20 

07-57 

2 

1 

11-45 

2 

1 

15-33 

07-70 

3 

1 

11-58 

3 

1 

15-46 

07-83 

4 

1 

11-71 

4 

1 

15-59 

07-96 

5 

1 

11-84 

5 

1 

15-72 

08-09 

6 

1 

11-97 

6 

1 

15-85 

08-22 

7 

1 

12-10 

7 

1 

15-98 

08-35 

8 

1 

12-23 

8 

1 

16-11 

08-48 

9 

1 

12-36 

9 

1 

16-23 

b' 

ST 

1 

CO 

1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 


JESSES  OP  SILVER  AND  GOLD  EXTRACTION. 

Silver  per  Ounce  Troy  at  different  Fineness. 


•930 
1 
2 
3 
4 
5 
6 
7 
8 
9 

•940 
1 
2 
3 
4 
5 
6 
7 
8 
9 

•950 
1 

2 
3 
4 
5 
6 
7 
8 
9 


20-24 
20-37 
20-50 
20-63 
20-76 

20-  89 

21-  02 
21-15 
21-28 
21-41 
21-54 
21-66 
21-79 

21-  92 

22-  05 
22-18 
22-31 
22-44 
22-57 
22-70 
22-83 

22-  96 

23-  09 
23-22 
23-35 
23-47 
23-60 
23-73 
23-86 
23-99 


•960 
1 

2 
3 
4 
5 
6 
7 
8 
9 

•970 
1 

2 
3 
4 
5 
6 
7 
8 
9 

•980 
1 
2 
3 
4 
5 
6 
7 


PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  309 


Value  of  Silver  per  Ounce  Troy  at  different  Fineness. 


H 

b 

CO 

3 

-b 

■  3 

ra 

"D 

o 

S3 

co 

c_ 

o 
ti 

co 

3 

!+ 

o 

CO 

IT 

3 

0 

B 

/i 

3 

/> 

Pi 

CO 

CO 

N 

CO 

o 

5" 

Q 

3* 

CD 

•990 

1 

28-00 

•994 

1 

28-52 

•998 

1 

29-03 

1 

1 

28-13 

5 

1 

28-65 

9 

1 

29-16 

2 

1 

28-26 

6 

1 

28 

•78 

1000 

1 

29-29 

3 

1 

28-39 

7 

1 

28-90 

TABLE  III 

SHOWING  THE  VALUE  OF  GOLD  PER  OUNCE  TROY  AS  IT  IS 
ALLOYED  IN  THE  BAR. 


312  PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION. 


Value  of  Crold  per  Ounce  Troy  at  different  Fineness. 


"* 

/I 

-a 
3 
a 

3 

—. 

a 

'4 

3 

2 

JL 
2 

01  -03 

•030 

62-02 

•0£0 

1 

JL 

•001 

09-07 

1 

JL 

64-08 

i 

JL 

1 

JL 

9fM  0 

ZiU  JLU 

9 

M 

O-L-1  3 

v-±  JLO 

9 

66-15 

9 

1 

J. 

98-1  7 

Q 
O 

Ofi-90 

9 
O 

68-22 

9 
O 

1 

30-93 

A 
t: 

A 

70-28 

A 

1 

39-30 

OZi  Ox) 

O 

1  0-34 

JLU  O'i 

O 

72-35 

U 

1 

31-37 

a 
u 

1  9-40 

u 

74-42 

u 

1 

3£-4.9 

7 
l 

1 J.-47 

7 
I 

76-49 

1 

1 

38-^0 
OO  (JV 

Q 

a 

1£-^4. 
±0  O'i 

Q 

o 

78-55 

Q 

o 

1 

9 

1  ft.fiO 
±o  OU 

9 

80-62 

9 

1 

^  O-i 

•010 

20-67 

•040 

82-69 

•070 

1 

44-70 

1 

22-74 

1 

84-75 

1 

1 

46-77 

2 

24-81 

2 

86-82 

2 

1 

48-84 

3 

26-87 

3 

88 

•89 

3 

1 

50-90 

4 

28-94 

4 

90-96 

4 

1 

52-97 

5 

31-01 

5 

93-02 

5 

1 

55-04 

6 

33-07 

6 

95-09 

6 

1 

57-11 

7 

35-14 

7 

97-16 

7 

1 

59-17 

8 

37-21 

8 

99-22 

8 

1 

61-24 

9 

39-28 

9 

1 

01-29 

9 

1 

63-31 

•020 

41-34 

•050 

1 

03-36 

•080 

1 

65-37 

1 

43-41 

1 

1 

05-43 

1 

1 

67-44 

2 

45-48 

2 

1 

07-49 

2 

1 

69-51 

3 

47-55 

3 

1 

09-56 

3 

1 

71-58 

4 

49-61 

4 

1 

11-63 

4 

1 

73-64 

5 

51-68 

5 

1 

13-70 

5 

1 

75-71 

6 

53-75 

6 

1 

15-76 

6 

1 

77-78 

7 

55-81 

7 

1 

17-83 

7 

1 

79-84 

8 

57-88 

8 

1 

19-90 

8 

1 

81-91 

9 

59-95 

9 

1 

21-96 

9 

1 

83-98 

p" 

H 

w 

1 
1 
1 
1 
1 
1 
1 

2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 


ESSES  OP  SILVER  AND  GOLD  EXTRACTION.  313 

Gold  per  Ounce  Troy  at  different  Fineness. 


O 

7) 

o 

o 

o 

f» 
o 

tr 
o 
P 
SO 

o 
p" 

H 

CO 

2 

ja 

© 
p 

t» 
p 

p* 

CO 

0 

CO 

S3 
pi 

5* 

co 

ndths  ] 

w 

p' 

p" 

* 

86-05 

•120 

2 

4o*Ub 

•1  ^0 

lOv 

3 

10-08 

88 

•11 

1 

2 

rA  -i  o 

oU-lo 

1 
1 

3 

12-14 

9048 

2 

2 

CO  OA 

o 
z 

3 

14-21 

92-25 

3 

2 

C  /I  0/2 

o4-zb 

q 
o 

3 

16-28 

94-32 

4 

2 

C£?  oo 
OD-OO 

3 

18-35 

96-38 

5 

2 

CO    A  f\ 

O 

3 

20-41 

98-45 

6 

2 

a  a  a  a 
b0*4b 

0 

3 

22-48 

00-52 

7 

2 

£JO  CO 

7 
l 

3 

24-55 

AO  cq 
VZ'OO 

8 

2 

b4-b(J 

Q 
O 

3 

26-61 

04-65 

9 

2 

bb-b  J 

Q 

3 

28-68 

06-72 

•130 

2 

68-73 

.1  AH 
100 

3 

30-75 

08-79 

1 

2 

70-80 

1 

3 

32-82 

10-85 

2 

2 

72-87 

9 
Z 

3 

34-88 

12-92 

3 

2 

74-94 

9 
O 

3 

36-95 

14-99 

4 

2 

77-00 

4 

3 

39-02 

17-05 

5 

2 

79-07 

5 

3 

41-09 

19-12 

6 

2 

81-14 

6 

3 

43-15 

21-19 

7 

2 

83-20 

7 

3 

45-22 

23-26 

8 

2 

85-27 

8 

3 

47-29 

25-32 

9 

2 

87-34 

9 

3 

49-35 

27-39 

•140 

o 
Z 

89-41 

•170 

3 

51-42 

29-46 

1 

2 

91-47 

1 

3 

53-49 

31-52 

2 

2 

93-54 

2 

3 

55-56 

33-59 

3 

2 

95-61 

3 

3 

57-62 

35-66 

4 

2 

97-67 

4 

3 

59-69 

37-73 

5 

2 

99-74 

5 

3 

61-76 

39-79 

6 

3 

01-81 

6 

3 

63-82 

41-86 

7 

3 

03-88 

7 

3 

65-89 

43-93 

8 

3 

05-94 

8 

3 

67-96 

45-99 

9 

3 

08-01 

9 

3 

70-03. 

22 


y 

o 

CO 

r  ; 

3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 


ESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Gold  per  Ounce  Troy  at  different  Fineness. 


T> 
3 
0 

0 
7 

3 
= 
~f. 

r 

c_ 

f" 

X 

< 
< 

s 
1 

TO  Afl 

Oi  A 

4 

o4#ll 

.OA  A 

4 

yb'iz 

t  a  ^  a 

74-lb 

1 

A 

4 

OG  1  O 

-< 

1 

4 

no.i  a 

7b-zo 

A 

4 

QO.O/f 

oo-z4 

0 

A 

5 

AA  0£? 

to  on 

0 

0 

4 

A  A  O"! 

0 
0 

5 

AO  OQ 

OA  0£J 

4 

4 

A 

4 

5 

c\a  on 

OO  AO 

82-43 

r 
0 

4 

44*44 

r 
0 

5 

At?  /<  a 
Ub*4b 

O  A    C  A 

b 

4 

/<  f>  C1 

b 

5 

AO  CO 

op 

OD'OD 

7 

4 

4o-oo 

rr 
< 

5 

1  A  CO 

00  /*o 

88-63 

O 

8 

4 

CA  £C 

50-bo 

0 
0 

5 

lz-bb 

AA  T A 

90-70 

9 

4 

CO  T1 

n 

y 

5 

~l  1  TQ 

92-76 

•220 

4 

54-78 

•250 

5 

16-80 

94-83 

1 

4 

56-85 

1 

5 

18-86 

96-90 

2 

4 

58-91 

2 

5 

20-93 

98-97 

3 

4 

60-98 

3 

5 

23-00 

01-03 

4 

4 

63-05 

4 

25-06 

03-10 

5 

4 

65-12 

5 

- 

27-13 

05-17 

6 

4 

67-18 

6 

5 

29-20 

07-24 

7 

4 

69-25 

7 

5 

31-27 

09-30 

8 

4 

71-32 

8 

5 

33-33 

11-37 

9 

4 

73-39 

9 

5 

35-40 

13-44 

•230 

4 

75-45 

•260 

5 

37-47 

15-50 

1 

4 

77-52 

1 

5 

39-53 

17-57 

2 

4 

79-59 

2 

5 

41-60 

19-64 

3 

4 

81-65 

3 

5 

43-67 

21-71 

4 

4 

83-72 

4 

5 

45-74 

23-78 

5 

4 

85-79 

5 

5 

47-80 

25-84 

6 

4 

87-86 

6 

5 

49-87 

27-91 

7 

4 

89-92 

7 

5 

51-94 

29-97 

8 

4 

91-99 

8 

5 

54-01 

32-04 

9 

4 

94-06 

9 

5 

56-07 

o 

p* 
•-( 

cn 

5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
6 
6 
6 
6 
6 
6 
6 
6 
6 


3SSES  OF  SILVER  AND  GOLD  EXTRACTION.  315 

Gold  per  Ounce  Troy  at  different  Fineness. 


3^ 

IT 
H 

so 

3" 

« 

? 

3 
b 

C  O  ^  A 

58-14 

OAA 

•300 

6 

20-16 

•330 

6 

82-17 

n  f\  ct-i 

60-21 

1 

6 

act  aa 

22-22 

■4 
1 

( 

-> 

84-24 

net  OT 

62-27 

2 

( 

Ct  i  OA 

24-29 

Ct 

2 

6 

86-30 

C*  A  OA 

64-34 

o 

3 

6 

26-36 

Ct 

3 

6 

8* 

3-37 

C*C  A  1 

DD-41 

A 

4 

6 

oo  a  a 

28-42 

A 

4 

6 

90-44 

Q  Q  AO 

5 

6 

OA   A  A 

30-49 

5 

6 

92-51 

17  a  r  A 

70-54 

n 

6 

6 

o  ct  r  n 

32-56 

6 

6 

y4-o< 

fro  n-t 

72-61 

7 

6 

ct  a   n  ct 

34-63 

7 

6 

96-64 

74-68 

o 

8 

6 

on  nf\ 

36-69 

8 

o 

98-71 

7b-74 

9 

6 

no  *7 n 

38-76 

9 

7 

00-78 

78-81 

•310 

6 

40-83 

•340 

7 

02-84 

80-88 

1 

6 

42-89 

1 

7 

04-91 

82-95 

2 

6 

44-96 

2 

7 

06-98 

85-01 

3 

6 

47-03 

3 

7 

09-04 

87-08 

4 

( 

;» 

49-10 

4 

7 

11-11 

89-15 

5 

6 

51-16 

5 

7 

13-18 

91-21 

6 

6 

53-23 

6 

7 

15-25 

93-28 

7 

6 

55-30 

7 

7 

17-31 

95-35 

8 

6 

57-36 

8 

7 

19-38 

97-42 

9 

6 

59-43 

9 

7 

21-45 

99-48 

•320 

6 

61-50 

•350 

7 

23-51 

01-55 

1 

6 

63-57 

1 

7 

25-58 

03-62 

2 

6 

65-63 

2 

7 

27-65 

05-68 

3 

( 

i 

67-70 

3 

7 

29-72 

07-75 

4 

6 

69-77 

4 

7 

31-78 

09-82 

5 

( 

71-83 

5 

7 

33-85 

11-89 

6 

6 

73-90 

6 

7 

35-92 

13-95 

7 

6 

75-97 

7 

7 

37-98 

16-02 

8 

6 

78-04 

8 

7 

40-05 

18-09 

9 

6 

80-10 

9 

7 

42-12 

0 

cn 

7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
8 
8 
8 


ESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Gold  per  Ounce  Troy  at  different  Fineness. 


- 

s 

B 

a 
-t- 

n 

3 

3 
» 

a  a  .1  a 

A/2. OA 

.  4  OA 

•4ZU 

£Q.OO 
DO'ZZ 

4b'ZO 

1 

i 

5 

AQ.OT 

i 
1 

I 

TA.OQ 

/(Q.QO 

o 

8 

1U'o4 

o 

* 

(Z'OD 

rA.on 

o 
O 

I 

o 
O 

8 

*7 A  .AO 

74-4* 

oz-4o 

A 

4 

8 

1  4  .A  T 

14*4  < 

A 

4 

8 

la.  a  a 
( D*4y 

04*0^ 

r 
O 

8 

Id*o4 

0 

8 

<  O'OO 

oo-oy 

/j 

o 

8 

1  Q.df\ 

lo'OU 

a 
0 

1 

QA.£JO 

OO'OD 

IT 

7 

8 

OA.£T 

1 

1 

QO.£A 

oz-oy 

£  a.to 

o 

o 

8 

OO.T/1 

o 

o 

8 

o4*  <0 

oz  /  y 

y 

* 

z4'ol 

y 

8 

QA.QO 

oo-oz 

64-86 

•400 

26-87 

•430 

8 

88-89 

66-93 

1 

i 

i 

28-94 

1 

i 

90-96 

68-99 

2 

8 

31-01 

■  2 

8 

93-02 

71-06 

3 

8 

33-07 

3 

8 

95-09 

73-13 

4 

8 

35-14 

4 

8 

97-16 

75-19 

5 

8 

37-21 

5 

8 

99-22 

77-26 

6 

8 

39-28 

6 

9 

01-29 

79-32 

7 

J 

41-34 

7 

03-36 

81-39 

8 

* 

J 

43-41 

8 

05-43 

83-46 

9 

i 

45-48 

9 

9 

07-49 

fe5-53 

•410 

8 

47-55 

•440 

09-56 

87-60 

1 

8 

49-61 

1 

11-63 

89-66 

2 

51-68 

2 

9 

13-70 

91-73 

3 

i 

53-75 

3 

9 

15-76 

93-80 

4 

8 

55-81 

4 

17-83 

95-87 

5 

8 

57-88 

5 

9 

19-90 

97-93 

6 

8 

59-95 

6 

21-96 

00-00 

7 

< 

62-02 

7 

24-03 

02-07 

8 

3 

64-08 

8 

9 

26-10 

04-13 

9 

i 

3 

66-15 

9 

) 

28-17 

b 

o 

CO 

9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 
9 


ESSES  OF  SILVER  AND  GOLD  EXTRACTION.  317 

Gold  per  Ounce  Troy  at  different  Fineness. 


o 

CD 

b 

o 

CD 

3 

o 

CD 

CO 

CO 

c_ 
ET 

3 

0 

CO 

CO 

if 

? 

I 

P 

Pli 

-O 

& 

CO 

I 

Pi 

CO 

j 

• 

* 

• 

p* 

CD 

* 

• 

j 

3' 

CD 

I 
\ 

30-23 

•480 

9 

92-25 

•510 

1  A 
1U 

54-26 

32-30 

1 

9 

94-32 

1 

56-33 

34-37 

2 

9 

96-38 

2 

1  A 

58-40 

36-43 

3 

9 

98-45 

3 

1  A 

60-47 

38-50 

4 

10 

00-52 

4 

1  A 

62-53 

40-57 

5 

10 

02-58 

5 

1  A 

64-60 

42-64 

6 

1  a 

04-65 

6 

1  A 

66-67 

44-70 

7 

10 

06-72 

7 

1  A 

68-73 

46-77 

8 

10 

08-79 

8 

1  A 

70-80 

48-84 

9 

10 

10-85 

9 

1  A 

72-87 

50-90 

•490 

10 

12-92 

•520 

10 

74-94 

52-97 

1 

10 

14-99 

1 

10 

77-00 

55-04 

2 

10 

17-05 

2 

10 

79-07  - 

57-H 

3 

10 

19-12 

3 

10 

81-14 

59-17 

4 

10 

21-19 

4 

10 

83-20 

61-24 

5 

10 

23-26 

5 

10 

85-27 

63-31 

6 

10 

25-32 

6 

10 

87-34 

65-37 

7 

10 

27-39 

7 

10 

89-41 

67-44 

8 

10 

29-46 

8 

10 

91-47 

69-51 

9 

10 

31-52 

9 

10 

93-54 

<  l-oo 

•500 

10 

•OoU 

10 

yo-bl 

73-64 

1 

10 

35-66 

1 

10 

97-67 

75-71 

2 

10 

37-73 

2 

10 

99-74 

77-78 

3 

10 

39-79 

3 

11 

01-81 

79-84 

4 

10 

41-86 

4 

IX 

03-88 

81-91 

5 

10 

43-93 

5 

11 

05-94 

83-98 

6 

10 

45-99 

6 

11 

08-01 

86-05 

7 

10 

48-06 

7 

11 

10-08 

88-11 

8 

10 

50-13 

8 

11 

12-14 

90-18 

9 

10 

52-20 

9 

11 

14-21 

lue  oj 
U 

o 

w 

CO 

11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 
11 


ESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Gold  per  Ounce  Troy  at  different  Fineness. 


3 

■» 

3 

3 

v 

3 

Ji 

Thousandths  Fine  

- 

r_ 

D* 
-. 

J. 

o 
3 

16-28 

•570 

11 

78-29 

r*  r\  r\ 

•600 

12 

40-31 

18-35 

-< 
1 

11 

80-36 

1 

12 

A  C\   O  O 

42-38 

20-41 

2 

11 

82-43 

2 

12 

A  A     A  A 

44-44 

22-48 

3 

11 

84-50 

3 

12 

46-51 

24-55 

4 

ll 

86 

•56 

4 

12 

ao  rn 

48-58 

26-61 

5 

11 

88 

•63 

5 

12 

50-65 

28-68 

6 

11 

90-70 

6 

12 

52-71 

30-75 

7 

11 

92-76 

7 

12 

c  a  it  r> 

54-78 

32-82 

8 

11 

94-83 

8 

12 

56-85 

34-88 

9 

11 

96-90 

9 

12 

58-91 

36-95 

•580 

11 

98-97 

•610 

12 

60-98 

39-02 

1 

12 

01-03 

1 

12 

63-05 

41-09 

2 

12 

03-10 

2 

12 

65-12 

43-15 

3 

12 

05-17 

3 

12 

67-18 

45-22 

4 

12 

07-24 

4 

12 

69-25 

47-29 

5 

12 

09-30 

5 

12 

71-32 

49-35 

6 

12 

11-37 

6 

12 

73-39 

51-42 

7 

12 

13-44 

7 

12 

75-45 

53-49 

8 

12 

15-50 

8 

12 

77-52 

9 

12 

17-57 

9 

12 

79-59 

57-62 

•590 

12 

19-64 

•620 

12 

81-65 

59-69 

1 

12 

21-71 

1 

12 

83-72 

61-76 

2 

12 

23-77 

2 

12 

85-79 

63-82 

3 

12 

25-84 

3 

12 

87-86 

65-89 

4 

12 

27-91 

4 

12 

89-92 

67-96 

5 

12 

29-97 

5 

12 

91-99 

70-03 

6 

12 

32-04 

6 

12 

94-06 

72-09 

7 

12 

34-11 

7 

12 

96-12 

74-16 

8 

12 

36-18 

8 

12 

98-19 

76-23 

9 

12 

38 

•24 

9 

13 

00-26 

b 

? 

13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 


ESSES  OF  SILVEE  AND  GOLD  EXTRACTION.  319 

Gold  per  Ounce  Troy  at  different  Fineness. 


-i 

a 

n 

A 

o 
f> 

- 

7 

f\^i   O  O 

02-33 

n  n  r\ 

•660 

13 

f*  A    O  A 

64-34 

r>  r\  r\ 

•690 

14 

26-36 

04-39 

-t 
1 

^  o 

13 

66-41 

1 

i  A 

14 

a  o  a  a 

28-42 

Af*    A  C* 

Ob-46 

2 

^  o 

13 

r>  o  /I  o 

68-48 

2 

14 

OA    A  r\ 

30-49 

AO  CO 

08-53 

o 

3 

i  O 

13 

T  A  C  /I 

70-54 

3 

-t  4 

14 

32-t>6 

i  a  r  A 

10-59 

A 

4 

^  o 

13 

72-bl 

A 

4 

14 

o  a  r>  ct 

34-63 

12*66 

5 

-1  o 

13 

rr  I   £»  Q 

74-68 

5 

-t  A 

14 

36-69 

-i  a  rrcy 

14-7,3 

6 

-1  o 

13 

76-74 

6 

14 

O  O  rr  r> 

38-76 

-i  n  OA 

lb-80 

rr 

7 

-I  o 

13 

TO  01 

78-81 

rr 

7 

14 

A  A    O  O 

40-83 

^  o  on 

18-86 

o 

8 

-1  o 

13 

OA  o  o 

80-00 

o 

8 

14 

A  Ci  OA 

42-89 

20-93 

9 

13 

CiC%  AC 

82-95 

9 

44 

a  a  r\r> 

44-96 

23-00 

•670 

13 

85-01 

•700 

14 

47-03 

25-06 

1 

13 

87-08 

1 

14 

49-10 

27-13 

2 

13 

89-15 

2 

14 

51-16 

29-20 

3 

13 

91-21 

3 

14 

53-23 

31-27 

4 

13 

93-28 

4 

14 

55-30 

33-33 

5 

13 

95-35 

5 

14 

57-36 

35-40 

6 

13 

97-42 

6 

14 

59-43 

37-47 

7 

13 

99-48 

7 

14 

61-50 

39-53 

8 

14 

01-55 

8 

14 

63-57 

41-60 

9 

14 

03-62 

9 

14 

65-63 

43-67 

•680 

14 

05-68 

•710 

14 

67-70 

45-74 

1 

14 

07-75 

1 

14 

69-76 

47-80 

2 

14 

09-82 

2 

14 

71-83 

49-87 

3 

14 

11-89 

3 

14 

73-90 

51-93 

4 

14 

13-95 

4 

14 

75-97 

54-01 

5 

14 

16-02 

5 

14 

78-04 

56-07 

6 

14 

18-09 

6 

14 

80-10 

58-14 

7 

14 

20-16 

7 

14 

82-17 

60-21 

8 

14 

22-22 

8 

14 

84-24 

62-27 

9 

14 

24-29 

9 

14 

86-30 

W 

o 

s 

14 
14 
14 
14 
14 
14 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 


ESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Gold  per  Ounce  Troy  at  different  Fineness. 


s 

r 

~~ 

d 

3 

O 
g 

CO 

; 
• 

i 

88-a7 

•750 

-1  C 

15 

C  A  OA 

50-39 

IT  O  A 

•780 

16 

 _ 

12-40 

90-44 

1 

lb 

52-45 

1 

16 

14-47 

92-51 

o 

2 

15 

54*52 

Ct 

Jt 

16 

16-54 

A  A    C  T 

94-57 

3 

15 

cr>  c a 

6 

16 

18-60 

n  r>  oa 

96-64 

A 

4 

15 

D8-66 

A 

4 

16 

20-67 

98-71 

5 

15 

/? A  TO 

bO-72 

5 

16 

22-74 

00-78 

6 

Id 

£JO  T A 

62-79 

6 

16 

24-81 

02-84 

7 

15 

64-86 

IT 

7 

16 

26-87 

04-91 

8 

15 

66-93 

8 

16 

28-94 

06-98 

9 

-I  c 

15 

(*  O  A  A 

68*99 

9 

16 

31-01 

09-04 

•760 

15 

71-06 

•790 

16 

33-07 

11-11 

1 

15 

73-13 

1 

16 

35-14 

13-18 

2 

15 

75-19 

2 

16 

37-21 

15-25 

3 

15 

77-26 

3 

16 

39-28 

17-31 

4 

15 

79-33 

4 

16 

41-34 

19-38 

5 

15 

81-40 

5 

16 

43-41 

21-45 

6 

15 

83-46 

6 

16 

45-48 

23-51 

7 

15 

85-53 

7 

16 

47-55 

25-58 

8 

15 

87-60 

8 

16 

49-61 

27-65 

9 

15 

89-66 

9 

16 

51-68 

29-72 

•770 

15 

91-73 

•800 

16 

53-75 

31-78 

1 

15 

93-80 

1 

16 

55-81 

33-85 

2 

15 

95-87 

2 

16 

57-88 

35-92 

3 

15 

97-93 

3 

16 

59-95 

37 

•98 

4 

16 

00-00 

4 

16 

62-02 

40-05 

5 

16 

02-07 

5 

16 

64-08 

42-12 

6 

16 

04-13 

6 

16 

66-15 

44-18 

7 

16 

06-20 

7 

16 

68-22 

46-25 

8 

16 

08-27 

8 

16 

70-28 

48-32 

9 

16 

10-34 

9 

16 

72-35 

PROCESSES  OF  SILVER  AND  GOLD  EXTRACTION.  321 

Value  of  Gold  per  Ounce  Troy  at  different  Fineness. 


a 

p 
7. 

-5 

T> 
3 
y. 

< 

V 

3 
■+ 

A 

a 

z 

T 

A 

( 

i 

3 

•810 

16 

74-42 

O  A  A 

•840 

17 

36-43 

OTA 

•870 

17 

no  a  cr 

98-4o 

1 

16 

76-49 

1 

17 

38-50 

■A 

1  1 

18 

00-52 

2 

lb 

78-55 

2 

17 

40-57 

2 

18 

AO  CO 

02-58 

3 

16 

80-62 

o 

3 

17 

42-64 

o 

3 

18 

a  i  o  c 

04-65 

4 

16 

82-69 

A 

4 

17 

A  A  A 

44-70 

4 

18 

A/^  I7fl 

06-72 

r 

5 

lo 

84-75 

5 

17 

A  r*  rrrr 

46-77 

r 

0 

-t  o 

18 

AO   17  A 

08-79 

6 

16 

86-82 

6 

17 

4  O  OA 

48-84 

rt 

6 

18 

10-8o 

7 

16 

88 

•89 

7 

-1  it 

17 

50-90 

7 

18 

12-92 

8 

16 

90-96 

8 

17 

52-97 

8 

18 

14-99 

9 

16 

93-02 

9 

17 

5o-04 

9 

18 

^  T  AC 

17-05 

•820 

16 

95-09 

•850 

17 

57-11 

•880 

18 

19-12 

1 

16 

97-16 

1 

17 

59-17 

1 

18 

21-19 

2 

16 

99-22  ! 

2 

17 

61-24 

2 

18 

23-26 

3 

17 

01-29 

3 

17 

63-31 

3 

18 

25-32 

4 

17 

03-36 

4 

17 

65-37 

4 

18 

27-39 

5 

17 

05-43 

5 

17 

67-44 

0 

18 

29-46 

6 

17 

07-49  ! 

6 

17 

69-51 

6 

18 

31-52 

7 

17 

09-56 

7 

17 

71-58 

7 

18 

33-59 

8 

17 

11-63 

8 

17 

73-64 

8 

18 

35-66 

9 

17 

13-70 

9 

17 

75-71 

9 

18 

37-73 

•830 

17 

15-76 

•860 

17 

77-78 

•890 

18 

39-79 

1 

17 

17-83 

1 

17 

79-84 

1 

18 

41-86 

2 

17 

19-90 

2 

17 

81-91 

2 

18 

43-93 

3 

17 

21-96 

3 

17 

83-98 

3 

18 

45-99 

4 

17 

24-03 

4 

17 

86-05 

4 

18 

48-06 

5 

17 

26-10 

5 

17 

88-11 

5 

18 

50-13 

6 

17 

28-17 

6 

17 

90-18 

6 

18 

52-20 

7 

17 

30-23 

7 

17 

92-25 

7 

18 

54-26 

8 

17 

32-30 

8 

17 

94-32 

8 

18 

56-33 

9 

17 

34-37 

9 

17 

96-38 

9 

18 

58-40 

23 


o 

? 
• 

18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
18 
19 
19 
19 
19 
19 
19 
19 
19 
19 
19 


ESSES  OF  SILVER  AND  GOLD  EXTRACTION. 

Gold  per  Ounce  Troy  at  different  Fineness. 


o 

o 

d 

O 

o 

H 

ST 

=1 

o 

o 

cn 

; 
; 

3" 

a 

• 
* 

p" 
1 

s 
I 

: 
■ 

* 

60-46 

no  a 

•930 

1  a 

22-48 

AP  A 

1  A 

iy 

84-50 

62-53 

1 

i  A 

19 

24-55 

1 

-l  A 

19 

86-56 

64-60 

2 

1  A 

19 

26-61 

2 

-\  A 

iy 

88-63 

66-67 

6 

"1  A 

iy 

28-68 

o 
6 

i  A 

iy 

90-70 

68-73 

A 

4 

"1  A 

19 

30-75 

4 

"1  A 

iy 

92-76 

70-80 

5 

i  A 

19 

32-82 

r 

0 

1  A 

iy 

94-83 

72-87 

n 
0 

1  A 

19 

34-88 

/-» 
0 

1  A 

iy 

96-90 

74-94 

7 

i  A 

19 

36-95 

7 

-|  A 

19 

98-97 

77-00 

o 

8 

1  A 

19 

39-02 

o 

8 

AA 

20 

01-03 

79-07 

9 

"1  A 

19 

41-08 

9 

A  A 

20 

03-10 

8144 

1Q 

-Li/ 

43-15 

•Q70 

V  I  V 

05-17 

83-20 

1 

19 

45-22 

1 

20 

07-23 

85-27 

2 

19 

47-29 

2 

20 

09-30 

87-34 

3 

19 

49-35 

3 

20 

11-37 

89-41 

4 

19 

51-42 

4 

20 

13-44 

91-47 

5 

19 

53-49 

5 

20 

15-50 

93-54 

6 

19 

55-56 

6 

20 

17-57 

95-61 

7 

19 

57-62 

7 

20 

19-64 

97-67 

8 

19 

59-69 

8 

20 

21-70 

99-74 

9 

19 

61-76 

9 

20 

23-77 

01-81 

•950 

19 

63-82 

•980 

20 

25-84 

03-88 

1 

19 

65-89 

1 

20 

27-91 

05-94 

2 

19 

67-96 

2 

20 

29-97 

08-01 

3 

19 

70-03 

3 

20 

32-04 

10-08 

4 

19 

72-09 

4 

20 

34-11 

12-14 

5 

19 

74-16 

5 

20 

36-18 

14-21 

6 

19 

76-23 

6 

20 

38-24 

16-28 

7 

19 

78-29 

7 

20 

40-31 

18-35 

8 

19 

80-36 

8 

20 

42-38 

20-41 

9 

19 

82-44 

9 

20 

44-44 

PROCESSES  OP  SILVER  AND  GOLD  EXTRACTION.  323 


Value  of  Gold  per  Ounce  Troy  at  different  Fineness. 


b 

3 

9 

L3 
~ 

b 

CD 

* 

3 

9 

cr 
o 

a 

w 

c 

p* 
►i 

■ 

O 
C 

CO 

| 

3 

O 

a 

CO 

D 

3 
o 

p 

o* 

BP 

P 
5 
Oi 

50 

p 

-?* 

CO 

CO 

CO 

N 

g 

6" 

o 

5* 

r 

5' 

•990 

20 

46-51 

•994 

20 

54-78 

•998 

20 

63-05 

1 

20 

48-58 

5 

20 

56-85 

9 

20 

65-12 

2 

20 

50-65 

6 

20 

58-91 

1000 

20 

67-18 

3 

20 

52-71 

7 

20 

60-98 

INDEX. 


Page. 

Abstrich  238 

Abzug   238 

Acetate  of  lead   192 

Acid,  sulphuric   71 

Acid,  hydrochloric   96 

Agitator  120,  173 

Alum   71 

Amalgamation  of  gold   59 

Amalgamation  of  gold  in  arrastras.. ..  61 
Amalgamation  of  gold  in  batteries.. ..  59 

Amalgamation  of  gold  in  pans   63 

Amalgamation  of  silver  261 

Amalgamation  of  silver  in  barrels.  117,  262 

Amalgamation  of  silver  in  pans  76,  124 

Amalgamation  of  silver  in  Veatch's 

Tubs   122 

Amalgamation  of  silver  in  Wheeler's 

Pans   81 

Amalgamation  of  copper  matt  267 

Amalgamation  of  speiss  268 

Amalgamation  of  black  copper  268 

Analysis  of  amalgam  and  bullion  metal  26 

Annealing  of  crucibles   135 

Antimonial  blend   41 

Antimonial  silver   45 

Argentiferous  copper  ore   190 

Argentiferous  gray  copper  ore   42 

Argentiferous  lead  ores   190 

Argentiferous  pyrites   191 

Argentiferous  zinc  ores   191 

Arsenical  blend   42 

Arquirite   47 

Assay  of  silver  with  the  blowpipe.. 28, 199 

Assay  of  silver  by  fire  48,  192 

Assay  of  silver  and  gold   50 

Assay  of  lead   57 

Assay  of  rich  silver  ores   193 

AsBay  of  silver  with  lead   193 


Pago. 

Assay  of  silver  without  lead   195 

Assay  of  silver  with  litharge  or  acetate 

of  lead   195 

Assay  of  roasted  ores   196 

Assay  of  poor  ores   196 

Assay  of  ores  rich  in  sulphurets  196 

Assay  of  ores  rich  in  earths  196 

Assay  of  alloys   197 

Assay  of  silver  and  lead   197 

Assay  of  silver,  tin,  and  zinc   197 

Assay  of  silver,  copper,  and  brass  198 

Assay  of  cupriferous  silver  198 

Assay  in  the  wet  way   199 

,A.ssay  for  matt  227 

Augustin's  Process  270 

Bismuth  silver   47 

Bisulphate  of  soda   11 

Blast  furnaces   146 

Blend,  antimonial   41 

Blend,  arsenical   42 

Blowpipe,  use  of   15 

Borax   10 

Borax  glass   11 

Brightening  241 

Brittle  silver  ore   40 

Bromic  silver   44 

Bromyrite   44 

Calomel   106 

Chemical  action  265 

Chemicals  69,  83 

Chemicals  per  ton  of  ore   74 

Chloride  of  silver   43 

Chlorination,  of  gold  ores   64 

Chlorine,  action  on  metals  65,  94 

Chlorobromide  of  silver   44 

Coating,  on  charcoal   17 

Concentration  of  silver  in  lead  164,  244 

Concentration  of  silver  in  zinc  249 


326 


INDEX. 


Page. 

Consume,  of  quicksilver   130 

Copperas   71 

Copper,  black   231 

Copper,  chloride  of   72 

Copper  dissolving  process   234 

Copper,  oxyd  of   12 

Copper,  subcbloride  of   73 

Copper,  sulphate  of   69 

Crucible  furnace   179 

Crucible  cast  iron   259 

Cupels   49 

Cupels,  size  of   198 

Cupel  mass  184,  236 

Cupellation  with  blowpipe   31 

Cupellation  under  muffle  53,  194 

Cupellation  on  hearth  154,235 

Cupelling  furnace   183 

Dark  red  silver  ore   41 

Division  of  silver  ores   189 

Dressing  of  assay  samples   199 

Embolite   44 

Eucairite   46 

Eugen-glance   40 

Examination  of  ores  for  roasting   98 

Examination  on  charcoal   16 

Examination  with  soda  and  borax   18 

Examination  in  a  closed  glass  tube   20 

Examination  in  an  open  glass  tube.. ..  22 

Extraction  of  gold   59 

Extraction  of  silver,  methods   205 

Extraction  of  silver  in  the  dry  way...  216 

Extraction  of  silver  with  lead   216 

Extraction  of  silver  from  lead  with  zinc  249 

Extraction  of  silver  in  the  wet  way..  261 

Extraction  of  silver  by  precipitation..  270 

Extraction  of  silver  from  copper  matt.  270 

Filtering  apparatus   274 

Flame   15 

Fluxes  for  melting  ores   148 

Froth  ,  155,  238,  242 

Furnace  for  assays   52 

Furnace  for  cupellation   183 

Furnace  for  meting  bars  135,  179 

Furnace  for  melting  ores   180 

Furnace  for  refining  silver   186 

Furnace  for  roasting  ores  176,  177 

Galvanic  action   266 

Gold   36 

Gold  with  mercury   37 

Gold  with  silver   36 

Gold  with  tellurium   37 

Gold  with  tellurium  and  lead   37 


Page. 

Granulation  of  lead   149 

Hardness  of  silver  ores   35 

Hearth  243 

Hessite   46 

Horn  silver   43 

Hydrostatic  melting  229 

Hyposulphite  of  6oda  279 

|  Incorporation   131 

j  Iodyrite   44 

J  Iodido  of  silver  and  mercury   45 

|  Iron,  protochlorid  of   73 

,  Iron,  chlorid  of   74 

;  Iron,  as  chemical   84 

j  Lead,  for  cupriferous  assays  198,  200 

I  Light  red  silver  ore   42 

|  Limadura   131 

!  Liquation   231 

Litharge   148 

Litharge  ring   157 

Litharge  fumes   158 

Litharge  black  238 

;  Litharge  red   242 

i  Litharge  yellow  242 

Lixiviation   273 

|  Loss  of  lead,  remedy  for   218 


;  Loss  of  silver  in  roasting   115 

'  Lustre  of  ores   24 

j  Magistral   129 

]  Marl  184  ,  236 

I  Matt  136,  226 

,  Melting  of  retorted  amalgam.  134,  138,  139 

Melting  of  silver  ores  with  lead  205 

!  Melting  of  rich  ores  in  crucibles  220 

i  Melting  in  cupelling  furnaces  221 

Melting  of  unroasted  ores  222 

Melting  of  roasted  argentiferous  cop- 
per ores  224 

Melting  of  rich  silver  ores   152 

Melting  furnace   180 

Melting  process   145 

Methods  of  extraction,  choice  of  218 

Methods,  principal  211 

Methods  of  refining  254 

Miargyrite   41 

Mixture  of  ore  for  melting...  151,  222,  223 

Xaumannite   46 

Oxydizing  flame   15 

Pans,  description  of  169,  170,  174 

Parke's  process  for  desilverising  lead..  249 
Patera's  process  for  extraction  of  sil- 
ver  279 


INDEX. 


327 


Page. 

Patio,  or  American  heap  amalgama- 
tion 164,  244 

Pattinson's  concentration  of  silver  in 

lead  164,  244 

Polybasite   40 

Polysulphide  of  sodium  279 

Proustite   42 

Protocbloride  of  iron   73 

Purification  of  lead   167 

Pyrargyrite   41 

Reagents  for  blowpipe  10,  12 

Reduction  flame   15 

Reduction  of  litharge   161 

Refining  of  silver  162,  251 

Refining  in  crucibles  162,  259 

Refining  in  hearth  furnaces   163 

Refining  on  movable  tests  254 

Refining  under  muflles  255 

Refining  in  reverberatory  furnaces   257 

Refining  furnace   186 

Retorting   133 

Roasting   90 

Roasting  for  barrel  amalgamation.  101,  263 

Roasting  for  pan  amalgamation   106 

Roasting  for  patio  process   129 

Roasting  for  Augustin's  process  271 

Roasting  for  Ziervogel's  process  276 

Roasting  for  Patera's  process   280 

Roharbeit  225 

Rohstein  225 

Ruby  silver  (see  pyrargyrite)   41 

Salt,  common  72,  96,  130 

Scheme  of  Pattinson's  crystallization..  248 

Scorification,  assay   193 

Scrapings  155,  23S 

Selenid  of  silver   46 

Selenid  of  silver  and  copper   46 

Separation  of  lead  and  silver  amal- 
gam   113 

Sign  of  completed  roasting  277 

Silver  amalgam   47 

Silver  assay   192 

Silver  bromic   44 

Silver,  chlorid  of   43 

Silver  chlorobromid   44 

Silver  copper  glance   39 


Page. 

Silver  fahlerz   42 

Silver  glance   38 

Silver,  iodid  of   44 

Silver  native   38 

Silver  ores   38 

Silver,  sulphuret  of   38 

Silver,  tellurid  of.   46 

Silver  concentration  in  matt  225 

Silver  concentration  in  lead  164,  244 

Silver  concentration  in  zinc  249 

Silver  extraction  by  mercury  207 

Silver  extraction  by  precipitation  208 

Silver  extraction  by  lead   228 

Skimmer   136 

Soda  bisulphate  11,  71 

Soda  carbonate  11,  49 

Specific  gravity   33 

Spitting  of  silver  253 

Spitting  of  silver,  remedy  for  257 

Steam  application  in  roasting   100 

Sternbergite   39 

Stromeyerite   39 

Sublimation  in  glass  tubes   21 

Sulphuret  of  silver  and  iron   39 

Systematic  proceeding  in  determining 

gold  and  silver  ores   23 

Table,  loss  of  silver  by  cupellation. ..  33 

Table,  progress  of  enriching  lead  165 

Tailings  80,  89,  108 

Temperature  in  cupelling  157,  258 

Tellurid  of  silver   46 

Test-ring  243 

Tinfoil   12 

Torta   131 

Treatment  of  slag  and  matt  from  melt- 
ing bars   141 

Treatment  of  rich  silver  ores  125,  209 

Treatment  of  poor  silver  ores  210 

Value  of  gold  and  silver  per  ounce —  145 

Vitriol  blue  \   69 

Vitriol  green   71 

Volatility  of  silver   100 

Weights,  for  assay   13 

Wet  assay   199 

Wet  process   67 

Xanthocone   42 


Fishb ouma's  Li th o £. 52 9  Clay  S t.  SX 


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Scale  /'h/.i  22.  23  '4  inc/i  totfzes/freti 

pshbonrrififs  Litk>tf5L'9  CIaySt.S  F 


% 


PLATE  VI. 


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» 


ft 


j 


PLATE IX- 


PLATE  XI. 


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